From c813a45eb13312cb31135d9d49c998280e75720c Mon Sep 17 00:00:00 2001
From: Leon van Kammen <leonvankammen@gmail.com>
Date: Fri, 20 Sep 2024 16:53:07 +0200
Subject: [PATCH] updated VP's in doc

---
 doc/RFC_XR_Fragments.html | 221 ++++++++++-----
 doc/RFC_XR_Fragments.md   |  62 ++++-
 doc/RFC_XR_Fragments.txt  | 552 +++++++++++++++++++++++++-------------
 doc/RFC_XR_Fragments.xml  | 214 ++++++++++-----
 4 files changed, 718 insertions(+), 331 deletions(-)

diff --git a/doc/RFC_XR_Fragments.html b/doc/RFC_XR_Fragments.html
index 6761da8..17aec4b 100644
--- a/doc/RFC_XR_Fragments.html
+++ b/doc/RFC_XR_Fragments.html
@@ -80,7 +80,7 @@ value:     draft-XRFRAGMENTS-leonvankammen-00
 
 <h1 class="special" id="abstract">Abstract</h1>
 
-<p>This draft is a specification for 4D URI&rsquo;s &amp; <a href="https://github.com/coderofsalvation/hypermediatic">hypermediatic</a> navigation, to enable a spatial web for hypermedia browsers with- or without a network-connection.<br>
+<p>This draft is a specification for interactive URI-controllable 3D files, enabling <a href="https://github.com/coderofsalvation/hypermediatic">hypermediatic</a> navigation, to enable a spatial web for hypermedia browsers with- or without a network-connection.<br>
 The specification uses <a href="https://www.w3.org/TR/media-frags/">W3C Media Fragments</a> and <a href="https://www.rfc-editor.org/rfc/rfc6570">URI Templates (RFC6570)</a> to promote spatial addressibility, sharing, navigation, filtering and databinding objects for (XR) Browsers.<br>
 XR Fragments allows us to better use existing metadata inside 3D scene(files), by connecting it to proven technologies like <a href="https://en.wikipedia.org/wiki/URI_fragment">URI Fragments</a>.<br>
 XR Fragments views spatial webs thru the lens of 3D scene URI&rsquo;s, rather than thru code(frameworks) or protocol-specific browsers (webbrowser e.g.).</p>
@@ -1281,90 +1281,97 @@ The XR Fragment-compatible browser can let the enduser access visual-meta(data)-
 <p>Environment mapping is crucial for creating realistic reflections and lighting effects on 3D objects.
 To apply environment mapping efficiently in a 3D scene, traverse the scene graph and assign each object&rsquo;s environment map based on the nearest ancestor&rsquo;s texture map. This ensures that objects inherit the correct environment mapping from their closest parent with a texture, enhancing the visual consistency and realism.</p>
 
-<p>&rdquo;&ldquo;&rdquo;
-  +&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash;+<br>
-  |                                |<br>
-  |  index.usdz                    |<br>
-  |    │                           |<br>
-  |    └── ◻ sphere (texture:foo)  |
-  |        └ ◻ cube (texture:bar)  | envMap = foo
+<pre><code>  +--------------------------------+  
+  |                                |  
+  |  index.usdz                    |  
+  |    │                           |  
+  |    └── ◻ sphere (texture:foo)  | 
+  |        └ ◻ cube (texture:bar)  | envMap = foo 
   |         └ ◻ cylinder           | envMap = bar
-  +&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&ndash;+</p>
-
-<pre><code>
-Most 3D viewers apply one and the same environment map for various models, however this logic 
-allows a more natural &amp; automatic strategy for reflection mapping. 
-
-# Transclusion (broken link) resolution
-
-In spirit of Ted Nelson's 'transclusion resolution', there's a soft-mechanism to harden links &amp; minimize broken links in various ways:
-
-1. defining a different transport protocol (https vs ipfs or DAT) in `src` or `href` values can make a difference
-2. mirroring files on another protocol using (HTTP) errorcode tags in `src` or `href` properties
-3. in case of `src`: nesting a copy of the embedded object in the placeholder object (`embeddedObject`) will not be replaced when the request fails
-
-&gt; due to the popularity, maturity and extensiveness of HTTP codes for client/server communication, non-HTTP protocols easily map to HTTP codes (ipfs ERR_NOT_FOUND maps to 404 e.g.)
-
-For example:
-
+  +--------------------------------+
 </code></pre>
 
-<p>+────────────────────────────────────────────────────────+
+<p>Most 3D viewers apply one and the same environment map for various models, however this logic
+allows a more natural &amp; automatic strategy for reflection mapping.</p>
+
+<h1 id="transclusion-broken-link-resolution">Transclusion (broken link) resolution</h1>
+
+<p>In spirit of Ted Nelson&rsquo;s &lsquo;transclusion resolution&rsquo;, there&rsquo;s a soft-mechanism to harden links &amp; minimize broken links in various ways:</p>
+
+<ol>
+<li>defining a different transport protocol (https vs ipfs or DAT) in <code>src</code> or <code>href</code> values can make a difference</li>
+<li>mirroring files on another protocol using (HTTP) errorcode tags in <code>src</code> or <code>href</code> properties</li>
+<li>in case of <code>src</code>: nesting a copy of the embedded object in the placeholder object (<code>embeddedObject</code>) will not be replaced when the request fails</li>
+</ol>
+
+<blockquote>
+<p>due to the popularity, maturity and extensiveness of HTTP codes for client/server communication, non-HTTP protocols easily map to HTTP codes (ipfs ERR_NOT_FOUND maps to 404 e.g.)</p>
+</blockquote>
+
+<p>For example:</p>
+
+<pre><code>  +────────────────────────────────────────────────────────+ 
   │                                                        │
   │  index.gltf                                            │
   │    │                                                   │
   │    │ #: #-offlinetext                                  │
   │    │                                                   │
   │    ├── ◻ buttonA                                       │
-  │    │      └ href:     <a href="http://foo.io/campagne.fbx">http://foo.io/campagne.fbx</a>       │
+  │    │      └ href:     http://foo.io/campagne.fbx       │
   │    │      └ href@404: ipfs://foo.io/campagne.fbx       │
   │    │      └ href@400: #clienterrortext                 │
   │    │      └ ◻ offlinetext                              │
   │    │                                                   │
-  │    └── ◻ embeddedObject                          &lt;&mdash;&mdash;&mdash; the meshdata inside embeddedObject will (not)
-  │           └ src: <a href="https://foo.io/bar.gltf">https://foo.io/bar.gltf</a>               │    be flushed when the request (does not) succeed.
-  │           └ src@404: <a href="http://foo.io/bar.gltf">http://foo.io/bar.gltf</a>            │    So worstcase the 3D data (of the time of publishing index.gltf)
-  │           └ src@400: <a href="https://archive.org/l2kj43.gltf">https://archive.org/l2kj43.gltf</a>   │    will be displayed.
+  │    └── ◻ embeddedObject                          &lt;--------- the meshdata inside embeddedObject will (not)
+  │           └ src: https://foo.io/bar.gltf               │    be flushed when the request (does not) succeed.
+  │           └ src@404: http://foo.io/bar.gltf            │    So worstcase the 3D data (of the time of publishing index.gltf)
+  │           └ src@400: https://archive.org/l2kj43.gltf   │    will be displayed.
   │                                                        │
-  +────────────────────────────────────────────────────────+</p>
-
-<pre><code>
-# Topic-based index-less Webrings 
-
-As hashtags in URLs map to the XWRG, `href`-values can be used to promote topic-based index-less webrings.&lt;br&gt;
-Consider 3D scenes linking to eachother using these `href` values:
-
-* `href: schoolA.edu/projects.gltf#math`
-* `href: schoolB.edu/projects.gltf#math`
-* `href: university.edu/projects.gltf#math`
-
-These links would all show visible links to math-tagged objects in the scene.&lt;br&gt;
-To filter out non-related objects one could take it a step further using filters:
-
-* `href: schoolA.edu/projects.gltf#math&amp;-topics math`
-* `href: schoolB.edu/projects.gltf#math&amp;-courses math`
-* `href: university.edu/projects.gltf#math&amp;-theme math`
-
-&gt; This would hide all object tagged with `topic`, `courses` or `theme` (including math) so that later only objects tagged with `math` will be visible 
-
-This makes spatial content multi-purpose, without the need to separate content into separate files, or show/hide things using a complex logiclayer like javascript.
-
-# URI Templates (RFC6570)
-
-XR Fragments adopts Level1 URI **Fragment** expansion to provide safe interactivity.&lt;br&gt;
-The following demonstrates a simple video player:
+  +────────────────────────────────────────────────────────+
 
 </code></pre>
 
-<p>+─────────────────────────────────────────────+
+<h1 id="topic-based-index-less-webrings">Topic-based index-less Webrings</h1>
+
+<p>As hashtags in URLs map to the XWRG, <code>href</code>-values can be used to promote topic-based index-less webrings.<br>
+Consider 3D scenes linking to eachother using these <code>href</code> values:</p>
+
+<ul>
+<li><code>href: schoolA.edu/projects.gltf#math</code></li>
+<li><code>href: schoolB.edu/projects.gltf#math</code></li>
+<li><code>href: university.edu/projects.gltf#math</code></li>
+</ul>
+
+<p>These links would all show visible links to math-tagged objects in the scene.<br>
+To filter out non-related objects one could take it a step further using filters:</p>
+
+<ul>
+<li><code>href: schoolA.edu/projects.gltf#math&amp;-topics math</code></li>
+<li><code>href: schoolB.edu/projects.gltf#math&amp;-courses math</code></li>
+<li><code>href: university.edu/projects.gltf#math&amp;-theme math</code></li>
+</ul>
+
+<blockquote>
+<p>This would hide all object tagged with <code>topic</code>, <code>courses</code> or <code>theme</code> (including math) so that later only objects tagged with <code>math</code> will be visible</p>
+</blockquote>
+
+<p>This makes spatial content multi-purpose, without the need to separate content into separate files, or show/hide things using a complex logiclayer like javascript.</p>
+
+<h1 id="uri-templates-rfc6570">URI Templates (RFC6570)</h1>
+
+<p>XR Fragments adopts Level1 URI <strong>Fragment</strong> expansion to provide safe interactivity.<br>
+The following demonstrates a simple video player:</p>
+
+<pre><code>
+  +─────────────────────────────────────────────+
   │                                             │
-  │   foo.usdz                                  │<br>
-  │     │                                       │<br>
-  │     │                                       │<br>
+  │   foo.usdz                                  │          
+  │     │                                       │          
+  │     │                                       │          
   │     ├── ◻ stopbutton                        │
   │     │      ├ #:    #-stopbutton             │
   │     │      └ href: #player=stop&amp;-stopbutton │  (stop and hide stop-button)
-  │     │                                       │<br>
+  │     │                                       │          
   │     └── ◻ plane                             │
   │            ├ play: #t=l:0,10                │
   │            ├ stop: #t=0,0                   │
@@ -1372,9 +1379,10 @@ The following demonstrates a simple video player:
   │            └ src:  cat.mp4#{player}         │
   │                                             │
   │                                             │
-  +─────────────────────────────────────────────+</p>
+  +─────────────────────────────────────────────+
 
-<p>&rdquo;`</p>
+
+</code></pre>
 
 <h1 id="additional-scene-metadata">Additional scene metadata</h1>
 
@@ -1499,11 +1507,90 @@ Therefore a 2-button navigation-interface is the bare minimum interface:</p>
 <li>the TTS reads the href-value (and/or aria-description if available)</li>
 </ol>
 
+<h2 id="xr-fragment-vendor-prefixes">XR Fragment Vendor Prefixes</h2>
+
+<p>Vendor Prefixes (XRFVP&rsquo;s) allows embedding a 3D file with popular 3D engines/framework-specific features via metadata:</p>
+
+<table>
+<thead>
+<tr>
+<th>what</th>
+<th>XR metadata</th>
+<th>Lowest common denominator</th>
+</tr>
+</thead>
+
+<tbody>
+<tr>
+<td>XR Fragments</td>
+<td>vendor-agnostic</td>
+<td>camera + 3D object(file) load/embed/click/referencing</td>
+</tr>
+
+<tr>
+<td>XR Fragments VP&rsquo;s</td>
+<td>vendor-<strong>specific</strong></td>
+<td>Entity-Component System (ECS)</td>
+</tr>
+</tbody>
+</table>
+<p>Vendor-specific metadata in a 3D scenefiles, are similar to vendor-specific <a href="https://en.wikipedia.org/wiki/CSS#Vendor_prefixes">CSS-prefixes</a> (<code>-moz-opacity: 0.2</code> e.g.).
+This allows popular 3D engines/frameworks, to initialize specific features when loading a scene/object, in a progressive enhanced way.</p>
+
+<blockquote>
+<p>Why? Because not all XR interactions can be solved/standardized by embedding XR Fragments into any 3D file.
+Some XR experiences need more than <strong>navigation</strong> and <strong>show/hide/filtering</strong> of objects (via click-state machines).
+The lowest common denominator between s that 3D engines use entity-component-system</p>
+</blockquote>
+
+<p>For example, the following metadata can be added to a .glb file, to make an object grabbable in AFRAME:</p>
+
+<pre><code>+────────────────────────────────────────────────────────────────────────────────────────────────────────+ 
+│ http://y.io/z.glb                             | AFRAME app                                             │ 
+│-----------------------------------------------+--------------------------------------------------------│ 
+│                                               |                                                        │
+│                                               | after loading the glb, john can be placed into the     │ 
+│     +-[3D mesh]-+                             | castle via hands, because the author added metadata to │  
+│     |    / \    |                             | john via either:                                       │  
+│     |   /   \   |                             |                                                        │ 
+│     |  /     \  |                             | 1. Blender (custom property-box, no plugins needed)    │ 
+│     |  |_____|  |                             |                                                        │  
+│     +-----│-----+                             | 2. javascript-code:                                    │  
+│           │                                   |                                                        │  
+│           ├─ name: castle                     |     for( var com in this.el.components ){              │  
+│           └─ tag: house baroque               |       this.el.object3D.userData[`-AFRAME-${com}`] = '' │  
+│                                               |     }                                                  │  
+│ [3D mesh-+                                    |     // save to z.glb in AFRAME inspector               │ 
+│ |        ├─ name: john                        |                                                        │  
+│ |    O   ├─ age: 23                           |                                                        │  
+│ |   /|\  ├─ -AFRAME-grabbable:      ''        | &gt; inits 'grabbable' component on object john           │ 
+│ |   / \  ├─ -AFRAME-material.color: '#F0A'    | &gt; inits 'material' component on object john            │  
+│ |        ├─ -AFRAME-text.value:  '{name}{age}'| &gt; inits 'text' component (*) with value 'john'         │  
+│ |        ├─ -THREE-material.fog: false        | &gt; changes material settings in THREE.js app            │ 
+│ |        ├─ -GODOT-Label3D.text: '{name}{age}'| &gt; inits 'Label3D' component (*) in Godot               │  
+│ +--------+                                    |                                                        │
+│                                               |                                                        │
+├─ -AFRAME-version: '1.6.0'                     | &gt;                                                      │
+├─ -GODOT-version:  '4.3'                       | &gt; exporters/authors can report targeted version        │
+│                                               |                                                        │
++────────────────────────────────────────────────────────────────────────────────────────────────────────+ 
+</code></pre>
+
+<ul>
+<li>key/value syntax: -<code>&lt;vendorname&gt;</code>-<code>&lt;component|version&gt;</code>.<code>&lt;key&gt;</code>  <code>[string/boolean/float/int]</code>-value</li>
+</ul>
+
+<p>String-templatevalues are evaluated as per <a href="https://www.rfc-editor.org/rfc/rfc6570">URI Templates (RFC6570)</a> Level 1.</p>
+
+<blockquote>
+<p>This &lsquo;separating of mechanism from policy&rsquo; (unix rule) does <strong>somewhat</strong> break portability of an XR experience, but still prevents (E-waste of) handcoded virtual worlds. It allows for (XR experience) metadata to survive in future 3D engines and scene-fileformats.</p>
+</blockquote>
+
 <h1 id="security-considerations">Security Considerations</h1>
 
 <p>The only dynamic parts are <a href="https://www.w3.org/TR/media-frags/">W3C Media Fragments</a> and <a href="https://www.rfc-editor.org/rfc/rfc6570">URI Templates (RFC6570)</a>.<br>
 The use of URI Templates is limited to pre-defined variables and Level0 fragments-expansion only, which makes it quite safe.<br>
-In fact, it is much safer than relying on a scripting language (javascript) which can change URN too.</p>
+n fact, it is much safer than relying on a scripting language (javascript) which can change URN too.</p>
 
 <h1 id="faq">FAQ</h1>
 
diff --git a/doc/RFC_XR_Fragments.md b/doc/RFC_XR_Fragments.md
index 8baba44..9e7ea06 100644
--- a/doc/RFC_XR_Fragments.md
+++ b/doc/RFC_XR_Fragments.md
@@ -93,7 +93,7 @@ value:     draft-XRFRAGMENTS-leonvankammen-00
 
 .# Abstract
 
-This draft is a specification for 4D URI's & [hypermediatic](https://github.com/coderofsalvation/hypermediatic) navigation, to enable a spatial web for hypermedia browsers with- or without a network-connection.<br> 
+This draft is a specification for interactive URI-controllable 3D files, enabling [hypermediatic](https://github.com/coderofsalvation/hypermediatic) navigation, to enable a spatial web for hypermedia browsers with- or without a network-connection.<br> 
 The specification uses [W3C Media Fragments](https://www.w3.org/TR/media-frags/) and [URI Templates (RFC6570)](https://www.rfc-editor.org/rfc/rfc6570) to promote spatial addressibility, sharing, navigation, filtering and databinding objects for (XR) Browsers.<br>
 XR Fragments allows us to better use existing metadata inside 3D scene(files), by connecting it to proven technologies like [URI Fragments](https://en.wikipedia.org/wiki/URI_fragment).<br>
 XR Fragments views spatial webs thru the lens of 3D scene URI's, rather than thru code(frameworks) or protocol-specific browsers (webbrowser e.g.).
@@ -791,7 +791,7 @@ For usecases like importing/exporting/p2p casting a scene, the issue of external
 Environment mapping is crucial for creating realistic reflections and lighting effects on 3D objects. 
 To apply environment mapping efficiently in a 3D scene, traverse the scene graph and assign each object's environment map based on the nearest ancestor's texture map. This ensures that objects inherit the correct environment mapping from their closest parent with a texture, enhancing the visual consistency and realism.
 
-``````
+```
   +--------------------------------+  
   |                                |  
   |  index.usdz                    |  
@@ -955,11 +955,67 @@ Therefore a 2-button navigation-interface is the bare minimum interface:
 2. objects with href metadata can be activated via a key (enter on a keyboard)
 3. the TTS reads the href-value (and/or aria-description if available)
 
+## XR Fragment Vendor Prefixes 
+
+Vendor Prefixes (XRFVP's) allows embedding a 3D file with popular 3D engines/framework-specific features via metadata:
+
+| what             | XR metadata         | Lowest common denominator                             |
+|------------------|---------------------|-------------------------------------------------------|
+| XR Fragments     | vendor-agnostic     | camera + 3D object(file) load/embed/click/referencing |
+| XR Fragments VP's| vendor-**specific** | Entity-Component System (ECS)                         |
+
+Vendor-specific metadata in a 3D scenefiles, are similar to vendor-specific [CSS-prefixes](https://en.wikipedia.org/wiki/CSS#Vendor_prefixes) (`-moz-opacity: 0.2` e.g.).
+This allows popular 3D engines/frameworks, to initialize specific features when loading a scene/object, in a progressive enhanced way.
+
+> Why? Because not all XR interactions can be solved/standardized by embedding XR Fragments into any 3D file.
+Some XR experiences need more than **navigation** and **show/hide/filtering** of objects (via click-state machines).
+The lowest common denominator between s that 3D engines use entity-component-system 
+
+For example, the following metadata can be added to a .glb file, to make an object grabbable in AFRAME:
+
+```
++────────────────────────────────────────────────────────────────────────────────────────────────────────+ 
+│ http://y.io/z.glb                             | AFRAME app                                             │ 
+│-----------------------------------------------+--------------------------------------------------------│ 
+│                                               |                                                        │
+│                                               | after loading the glb, john can be placed into the     │ 
+│     +-[3D mesh]-+                             | castle via hands, because the author added metadata to │  
+│     |    / \    |                             | john via either:                                       │  
+│     |   /   \   |                             |                                                        │ 
+│     |  /     \  |                             | 1. Blender (custom property-box, no plugins needed)    │ 
+│     |  |_____|  |                             |                                                        │  
+│     +-----│-----+                             | 2. javascript-code:                                    │  
+│           │                                   |                                                        │  
+│           ├─ name: castle                     |     for( var com in this.el.components ){              │  
+│           └─ tag: house baroque               |       this.el.object3D.userData[`-AFRAME-${com}`] = '' │  
+│                                               |     }                                                  │  
+│ [3D mesh-+                                    |     // save to z.glb in AFRAME inspector               │ 
+│ |        ├─ name: john                        |                                                        │  
+│ |    O   ├─ age: 23                           |                                                        │  
+│ |   /|\  ├─ -AFRAME-grabbable:      ''        | > inits 'grabbable' component on object john           │ 
+│ |   / \  ├─ -AFRAME-material.color: '#F0A'    | > inits 'material' component on object john            │  
+│ |        ├─ -AFRAME-text.value:  '{name}{age}'| > inits 'text' component (*) with value 'john'         │  
+│ |        ├─ -THREE-material.fog: false        | > changes material settings in THREE.js app            │ 
+│ |        ├─ -GODOT-Label3D.text: '{name}{age}'| > inits 'Label3D' component (*) in Godot               │  
+│ +--------+                                    |                                                        │
+│                                               |                                                        │
+├─ -AFRAME-version: '1.6.0'                     | >                                                      │
+├─ -GODOT-version:  '4.3'                       | > exporters/authors can report targeted version        │
+│                                               |                                                        │
++────────────────────────────────────────────────────────────────────────────────────────────────────────+ 
+```  
+
+* key/value syntax: -`<vendorname>`-`<component|version>`.`<key>`  `[string/boolean/float/int]`-value
+
+String-templatevalues are evaluated as per [URI Templates (RFC6570)](https://www.rfc-editor.org/rfc/rfc6570) Level 1. 
+
+> This 'separating of mechanism from policy' (unix rule) does **somewhat** break portability of an XR experience, but still prevents (E-waste of) handcoded virtual worlds. It allows for (XR experience) metadata to survive in future 3D engines and scene-fileformats.
+
 # Security Considerations
 
 The only dynamic parts are [W3C Media Fragments](https://www.w3.org/TR/media-frags/) and [URI Templates (RFC6570)](https://www.rfc-editor.org/rfc/rfc6570).<br>
 The use of URI Templates is limited to pre-defined variables and Level0 fragments-expansion only, which makes it quite safe.<br>
-In fact, it is much safer than relying on a scripting language (javascript) which can change URN too.
+n fact, it is much safer than relying on a scripting language (javascript) which can change URN too.
 
 # FAQ 
 
diff --git a/doc/RFC_XR_Fragments.txt b/doc/RFC_XR_Fragments.txt
index cb286da..7abb504 100644
--- a/doc/RFC_XR_Fragments.txt
+++ b/doc/RFC_XR_Fragments.txt
@@ -3,7 +3,7 @@
 
 
 Jens & Leon Internet Engineering Task Force              L.R. van Kammen
-Internet-Draft                                              12 July 2024
+Internet-Draft                                         20 September 2024
 Intended status: Informational                                          
 
 
@@ -13,10 +13,10 @@ Intended status: Informational
 
 Abstract
 
-   This draft is a specification for 4D URI's & hypermediatic
-   (https://github.com/coderofsalvation/hypermediatic) navigation, to
-   enable a spatial web for hypermedia browsers with- or without a
-   network-connection.
+   This draft is a specification for interactive URI-controllable 3D
+   files, enabling hypermediatic (https://github.com/coderofsalvation/
+   hypermediatic) navigation, to enable a spatial web for hypermedia
+   browsers with- or without a network-connection.
    The specification uses W3C Media Fragments (https://www.w3.org/TR/
    media-frags/) and URI Templates (RFC6570) (https://www.rfc-
    editor.org/rfc/rfc6570) to promote spatial addressibility, sharing,
@@ -46,16 +46,16 @@ Status of This Memo
    time.  It is inappropriate to use Internet-Drafts as reference
    material or to cite them other than as "work in progress."
 
-   This Internet-Draft will expire on 13 January 2025.
+   This Internet-Draft will expire on 24 March 2025.
 
 
 
 
 
 
-van Kammen               Expires 13 January 2025                [Page 1]
+van Kammen                Expires 24 March 2025                 [Page 1]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
 Copyright Notice
@@ -104,23 +104,27 @@ Table of Contents
      17.2.  URL and Data URI . . . . . . . . . . . . . . . . . . . .  29
    18. Importing/exporting . . . . . . . . . . . . . . . . . . . . .  30
    19. Reflection Mapping  . . . . . . . . . . . . . . . . . . . . .  30
-   20. Additional scene metadata . . . . . . . . . . . . . . . . . .  31
-   21. Accessibility interface . . . . . . . . . . . . . . . . . . .  33
+   20. Transclusion (broken link) resolution . . . . . . . . . . . .  30
+   21. Topic-based index-less Webrings . . . . . . . . . . . . . . .  31
 
 
 
-van Kammen               Expires 13 January 2025                [Page 2]
+van Kammen                Expires 24 March 2025                 [Page 2]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
-     21.1.  Two-button navigation  . . . . . . . . . . . . . . . . .  34
-   22. Security Considerations . . . . . . . . . . . . . . . . . . .  34
-   23. FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  34
-   24. authors . . . . . . . . . . . . . . . . . . . . . . . . . . .  35
-   25. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  35
-   26. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  35
-   27. Appendix: Definitions . . . . . . . . . . . . . . . . . . . .  35
+   22. URI Templates (RFC6570) . . . . . . . . . . . . . . . . . . .  32
+   23. Additional scene metadata . . . . . . . . . . . . . . . . . .  32
+   24. Accessibility interface . . . . . . . . . . . . . . . . . . .  33
+     24.1.  Two-button navigation  . . . . . . . . . . . . . . . . .  34
+     24.2.  XR Fragment Vendor Prefixes  . . . . . . . . . . . . . .  35
+   25. Security Considerations . . . . . . . . . . . . . . . . . . .  37
+   26. FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  37
+   27. authors . . . . . . . . . . . . . . . . . . . . . . . . . . .  37
+   28. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  38
+   29. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  38
+   30. Appendix: Definitions . . . . . . . . . . . . . . . . . . . .  38
 
 1.  Introduction
 
@@ -161,13 +165,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-
-
-
-
-van Kammen               Expires 13 January 2025                [Page 3]
+van Kammen                Expires 24 March 2025                 [Page 3]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    XR Fragments tries to seek to connect the world of text (semantical
@@ -221,9 +221,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025                [Page 4]
+van Kammen                Expires 24 March 2025                 [Page 4]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
  +───────────────────────────────────────────────────────────────────────────────────────────────+
@@ -277,9 +277,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025                [Page 5]
+van Kammen                Expires 24 March 2025                 [Page 5]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    *  allowing 3D assets/nodes to publish XR Fragments to themselves/
@@ -333,9 +333,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025                [Page 6]
+van Kammen                Expires 24 March 2025                 [Page 6]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    +=========+======================+=====================================+
@@ -389,9 +389,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025                [Page 7]
+van Kammen                Expires 24 March 2025                 [Page 7]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
 4.  Conventions and Definitions
@@ -445,9 +445,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025                [Page 8]
+van Kammen                Expires 24 March 2025                 [Page 8]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
   my.io/scene.fbx
@@ -501,9 +501,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025                [Page 9]
+van Kammen                Expires 24 March 2025                 [Page 9]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    |Media Fragments        |media fragment                        |#t=0,2&loop |play (and   |
@@ -557,9 +557,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 10]
+van Kammen                Expires 24 March 2025                [Page 10]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
 6.2.  Fragment-to-metadata mapping
@@ -613,9 +613,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 11]
+van Kammen                Expires 24 March 2025                [Page 11]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    |                |                                      |             |                     |metadata (bar:#t=0     |
@@ -669,9 +669,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 12]
+van Kammen                Expires 24 March 2025                [Page 12]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    | temporal  | s=x                  | 1             | set playback   |
@@ -725,9 +725,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 13]
+van Kammen                Expires 24 March 2025                [Page 13]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    |           |                      |               | uv             |
@@ -781,9 +781,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 14]
+van Kammen                Expires 24 March 2025                [Page 14]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
   +──────────────────────────────────────────────────────────+
@@ -837,9 +837,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 15]
+van Kammen                Expires 24 March 2025                [Page 15]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    1.  the Y-coordinate of pos identifies the floorposition.  This means
@@ -893,9 +893,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 16]
+van Kammen                Expires 24 March 2025                [Page 16]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    1.  IF a #cube matches a custom property-key (of an object) in the 3D
@@ -949,9 +949,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 17]
+van Kammen                Expires 24 March 2025                [Page 17]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
   +────────────────────────────────────────────────────────+  +─────────────────────────+
@@ -1005,9 +1005,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 18]
+van Kammen                Expires 24 March 2025                [Page 18]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    6.   <b>external</b> src values should be served with appropriate
@@ -1061,9 +1061,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 19]
+van Kammen                Expires 24 March 2025                [Page 19]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
        +==========+==================+============================+
@@ -1117,9 +1117,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 20]
+van Kammen                Expires 24 March 2025                [Page 20]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    » example implementation
@@ -1173,9 +1173,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 21]
+van Kammen                Expires 24 March 2025                [Page 21]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    *  calculate the <b>bounding box</b> of the instanced scene, and
@@ -1229,9 +1229,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 22]
+van Kammen                Expires 24 March 2025                [Page 22]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    |  NOTE: hardcoded framestart/framestop uses sampleRate/fps of
@@ -1285,9 +1285,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 23]
+van Kammen                Expires 24 March 2025                [Page 23]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
         +==========+==============================================+
@@ -1341,9 +1341,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 24]
+van Kammen                Expires 24 March 2025                [Page 24]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    7.   detect exclude keys like -foo (reference regex= /^-/ )
@@ -1397,9 +1397,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 25]
+van Kammen                Expires 24 March 2025                [Page 25]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    Instead of just throwing together all kinds media types into one
@@ -1453,9 +1453,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 26]
+van Kammen                Expires 24 March 2025                [Page 26]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
   http://y.io/z.fbx                                                           | Derived XRWG (expressed as JSON)
@@ -1509,9 +1509,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 27]
+van Kammen                Expires 24 March 2025                [Page 27]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    *  wordmatch *inside* src text
@@ -1565,9 +1565,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 28]
+van Kammen                Expires 24 March 2025                [Page 28]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
    *  out-of-the-box (de)multiplex human text and metadata in one go
@@ -1621,9 +1621,9 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 29]
+van Kammen                Expires 24 March 2025                [Page 29]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
 18.  Importing/exporting
@@ -1644,100 +1644,131 @@ Internet-Draft                XR Fragments                     July 2024
    from their closest parent with a texture, enhancing the visual
    consistency and realism.
 
-   `````` +--------------------------------+
-   | |
-   | index.usdz |
-   | │ |
-   | └── ◻ sphere (texture:foo) | | └ ◻ cube (texture:bar) | envMap =
-   foo | └ ◻ cylinder | envMap = bar +--------------------------------+
+     +--------------------------------+
+     |                                |
+     |  index.usdz                    |
+     |    │                           |
+     |    └── ◻ sphere (texture:foo)  |
+     |        └ ◻ cube (texture:bar)  | envMap = foo
+     |         └ ◻ cylinder           | envMap = bar
+     +--------------------------------+
 
-Most 3D viewers apply one and the same environment map for various models, however this logic
-allows a more natural & automatic strategy for reflection mapping.
+   Most 3D viewers apply one and the same environment map for various
+   models, however this logic allows a more natural & automatic strategy
+   for reflection mapping.
 
-# Transclusion (broken link) resolution
+20.  Transclusion (broken link) resolution
 
-In spirit of Ted Nelson's 'transclusion resolution', there's a soft-mechanism to harden links & minimize broken links in various ways:
+   In spirit of Ted Nelson's 'transclusion resolution', there's a soft-
+   mechanism to harden links & minimize broken links in various ways:
 
-1. defining a different transport protocol (https vs ipfs or DAT) in `src` or `href` values can make a difference
-2. mirroring files on another protocol using (HTTP) errorcode tags in `src` or `href` properties
-3. in case of `src`: nesting a copy of the embedded object in the placeholder object (`embeddedObject`) will not be replaced when the request fails
+   1.  defining a different transport protocol (https vs ipfs or DAT) in
+       src or href values can make a difference
+   2.  mirroring files on another protocol using (HTTP) errorcode tags
+       in src or href properties
+   3.  in case of src: nesting a copy of the embedded object in the
+       placeholder object (embeddedObject) will not be replaced when the
+       request fails
 
-> due to the popularity, maturity and extensiveness of HTTP codes for client/server communication, non-HTTP protocols easily map to HTTP codes (ipfs ERR_NOT_FOUND maps to 404 e.g.)
-
-For example:
-
-   +────────────────────────────────────────────────────────+ │ │ │
-   index.gltf │ │ │ │ │ │ #: #-offlinetext │ │ │ │ │ ├── ◻ buttonA │ │ │
-   └ href: http://foo.io/campagne.fbx (http://foo.io/campagne.fbx) │ │ │
-   └ href@404: ipfs://foo.io/campagne.fbx │ │ │ └ href@400:
-   #clienterrortext │ │ │ └ ◻ offlinetext │ │ │ │ │ └── ◻ embeddedObject
-   <--------- the meshdata inside embeddedObject will (not) │ └ src:
-   https://foo.io/bar.gltf (https://foo.io/bar.gltf) │ be flushed when
-   the request (does not) succeed.  │ └ src@404: http://foo.io/bar.gltf
+   |  due to the popularity, maturity and extensiveness of HTTP codes
+   |  for client/server communication, non-HTTP protocols easily map to
+   |  HTTP codes (ipfs ERR_NOT_FOUND maps to 404 e.g.)
 
 
 
-van Kammen               Expires 13 January 2025               [Page 30]
+
+van Kammen                Expires 24 March 2025                [Page 30]
 
-Internet-Draft                XR Fragments                     July 2024
+Internet-Draft                XR Fragments                September 2024
 
 
-   (http://foo.io/bar.gltf) │ So worstcase the 3D data (of the time of
-   publishing index.gltf) │ └ src@400: https://archive.org/l2kj43.gltf
-   (https://archive.org/l2kj43.gltf) │ will be displayed.  │ │
-   +────────────────────────────────────────────────────────+
+   For example:
 
-# Topic-based index-less Webrings
+  +────────────────────────────────────────────────────────+
+  │                                                        │
+  │  index.gltf                                            │
+  │    │                                                   │
+  │    │ #: #-offlinetext                                  │
+  │    │                                                   │
+  │    ├── ◻ buttonA                                       │
+  │    │      └ href:     http://foo.io/campagne.fbx       │
+  │    │      └ href@404: ipfs://foo.io/campagne.fbx       │
+  │    │      └ href@400: #clienterrortext                 │
+  │    │      └ ◻ offlinetext                              │
+  │    │                                                   │
+  │    └── ◻ embeddedObject                          <--------- the meshdata inside embeddedObject will (not)
+  │           └ src: https://foo.io/bar.gltf               │    be flushed when the request (does not) succeed.
+  │           └ src@404: http://foo.io/bar.gltf            │    So worstcase the 3D data (of the time of publishing index.gltf)
+  │           └ src@400: https://archive.org/l2kj43.gltf   │    will be displayed.
+  │                                                        │
+  +────────────────────────────────────────────────────────+
 
-As hashtags in URLs map to the XWRG, `href`-values can be used to promote topic-based index-less webrings.<br>
-Consider 3D scenes linking to eachother using these `href` values:
+21.  Topic-based index-less Webrings
 
-* `href: schoolA.edu/projects.gltf#math`
-* `href: schoolB.edu/projects.gltf#math`
-* `href: university.edu/projects.gltf#math`
+   As hashtags in URLs map to the XWRG, href-values can be used to
+   promote topic-based index-less webrings.
+   Consider 3D scenes linking to eachother using these href values:
 
-These links would all show visible links to math-tagged objects in the scene.<br>
-To filter out non-related objects one could take it a step further using filters:
+   *  href: schoolA.edu/projects.gltf#math
+   *  href: schoolB.edu/projects.gltf#math
+   *  href: university.edu/projects.gltf#math
 
-* `href: schoolA.edu/projects.gltf#math&-topics math`
-* `href: schoolB.edu/projects.gltf#math&-courses math`
-* `href: university.edu/projects.gltf#math&-theme math`
+   These links would all show visible links to math-tagged objects in
+   the scene.
+   To filter out non-related objects one could take it a step further
+   using filters:
 
-> This would hide all object tagged with `topic`, `courses` or `theme` (including math) so that later only objects tagged with `math` will be visible
+   *  href: schoolA.edu/projects.gltf#math&-topics math
+   *  href: schoolB.edu/projects.gltf#math&-courses math
+   *  href: university.edu/projects.gltf#math&-theme math
 
-This makes spatial content multi-purpose, without the need to separate content into separate files, or show/hide things using a complex logiclayer like javascript.
+   |  This would hide all object tagged with topic, courses or theme
+   |  (including math) so that later only objects tagged with math will
+   |  be visible
 
-# URI Templates (RFC6570)
+   This makes spatial content multi-purpose, without the need to
+   separate content into separate files, or show/hide things using a
+   complex logiclayer like javascript.
 
-XR Fragments adopts Level1 URI **Fragment** expansion to provide safe interactivity.<br>
-The following demonstrates a simple video player:
 
-   +─────────────────────────────────────────────+ │ │ │ foo.usdz │
-   │ │ │
-   │ │ │
-   │ ├── ◻ stopbutton │ │ │ ├ #: #-stopbutton │ │ │ └ href:
-   #player=stop&-stopbutton │ (stop and hide stop-button) │ │ │
-   │ └── ◻ plane │ │ ├ play: #t=l:0,10 │ │ ├ stop: #t=0,0 │ │ ├ href:
-   #player=play&stopbutton │ (play and show stop-button) │ └ src:
-   cat.mp4#{player} │ │ │ │ │
-   +─────────────────────────────────────────────+
 
-   ```
 
-20.  Additional scene metadata
+van Kammen                Expires 24 March 2025                [Page 31]
+
+Internet-Draft                XR Fragments                September 2024
+
+
+22.  URI Templates (RFC6570)
+
+   XR Fragments adopts Level1 URI *Fragment* expansion to provide safe
+   interactivity.
+   The following demonstrates a simple video player:
+
+  +─────────────────────────────────────────────+
+  │                                             │
+  │   foo.usdz                                  │
+  │     │                                       │
+  │     │                                       │
+  │     ├── ◻ stopbutton                        │
+  │     │      ├ #:    #-stopbutton             │
+  │     │      └ href: #player=stop&-stopbutton │  (stop and hide stop-button)
+  │     │                                       │
+  │     └── ◻ plane                             │
+  │            ├ play: #t=l:0,10                │
+  │            ├ stop: #t=0,0                   │
+  │            ├ href: #player=play&stopbutton  │  (play and show stop-button)
+  │            └ src:  cat.mp4#{player}         │
+  │                                             │
+  │                                             │
+  +─────────────────────────────────────────────+
+
+23.  Additional scene metadata
 
    XR Fragments does not aim to redefine the metadata-space or
    accessibility-space by introducing its own cataloging-metadata
    fields.  Instead, it encourages browsers to scan nodes for the
    following custom properties:
 
-
-
-van Kammen               Expires 13 January 2025               [Page 31]
-
-Internet-Draft                XR Fragments                     July 2024
-
-
    *  SPDX (https://spdx.dev/) license information
    *  ARIA (https://www.w3.org/WAI/standards-guidelines/aria/)
       attributes (aria-*: .....)
@@ -1751,6 +1782,18 @@ Internet-Draft                XR Fragments                     July 2024
    promotes accessibility and allows scene transcripts.  Please start
    aria-description with a verb to aid transcripts.
 
+
+
+
+
+
+
+
+van Kammen                Expires 24 March 2025                [Page 32]
+
+Internet-Draft                XR Fragments                September 2024
+
+
    |  Example: object 'tryceratops' with aria-description: is a huge
    |  dinosaurus standing on a #mountain generates transcript
    |  #tryceratops is a huge dinosaurus standing on a #mountain, where
@@ -1787,26 +1830,26 @@ Internet-Draft                XR Fragments                     July 2024
 
    |  * = these are interchangable (only one needs to be defined)
 
-
-
-van Kammen               Expires 13 January 2025               [Page 32]
-
-Internet-Draft                XR Fragments                     July 2024
-
-
    There's no silver bullet when it comes to metadata, so one should
    support where the metadata is/goes.
 
    |  These attributes can be scanned and presented during an href or
    |  src eye/mouse-over.
 
-21.  Accessibility interface
+24.  Accessibility interface
 
    The addressibility of XR Fragments allows for unique 3D-to-text
    transcripts, as well as an textual interface to navigate 3D content.
    Spec:
    <Br>
 
+
+
+van Kammen                Expires 24 March 2025                [Page 33]
+
+Internet-Draft                XR Fragments                September 2024
+
+
    1.   The enduser must be able to enable an accessibility-mode (which
         persists across application/webpage restarts)
    2.   Accessibility-mode must contain a text-input for the user to
@@ -1842,15 +1885,7 @@ Internet-Draft                XR Fragments                     July 2024
         https://.../... in case a 3D node exist with name abc and href
         value https://.../...
 
-
-
-
-van Kammen               Expires 13 January 2025               [Page 33]
-
-Internet-Draft                XR Fragments                     July 2024
-
-
-21.1.  Two-button navigation
+24.1.  Two-button navigation
 
    For specific user-profiles, gyroscope/mouse/keyboard/audio/visuals
    will not be available.
@@ -1864,17 +1899,136 @@ Internet-Draft                XR Fragments                     July 2024
    3.  the TTS reads the href-value (and/or aria-description if
        available)
 
-22.  Security Considerations
+
+
+van Kammen                Expires 24 March 2025                [Page 34]
+
+Internet-Draft                XR Fragments                September 2024
+
+
+24.2.  XR Fragment Vendor Prefixes
+
+   Vendor Prefixes (XRFVP's) allows embedding a 3D file with popular 3D
+   engines/framework-specific features via metadata:
+
+    +==============+===================+==============================+
+    | what         | XR metadata       | Lowest common denominator    |
+    +==============+===================+==============================+
+    | XR Fragments | vendor-agnostic   | camera + 3D object(file)     |
+    |              |                   | load/embed/click/referencing |
+    +--------------+-------------------+------------------------------+
+    | XR Fragments | vendor-*specific* | Entity-Component System      |
+    | VP's         |                   | (ECS)                        |
+    +--------------+-------------------+------------------------------+
+
+                                  Table 14
+
+   Vendor-specific metadata in a 3D scenefiles, are similar to vendor-
+   specific CSS-prefixes (https://en.wikipedia.org/wiki/
+   CSS#Vendor_prefixes) (-moz-opacity: 0.2 e.g.).  This allows popular
+   3D engines/frameworks, to initialize specific features when loading a
+   scene/object, in a progressive enhanced way.
+
+   |  Why?  Because not all XR interactions can be solved/standardized
+   |  by embedding XR Fragments into any 3D file.  Some XR experiences
+   |  need more than *navigation* and *show/hide/filtering* of objects
+   |  (via click-state machines).  The lowest common denominator between
+   |  s that 3D engines use entity-component-system
+
+   For example, the following metadata can be added to a .glb file, to
+   make an object grabbable in AFRAME:
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+van Kammen                Expires 24 March 2025                [Page 35]
+
+Internet-Draft                XR Fragments                September 2024
+
+
++────────────────────────────────────────────────────────────────────────────────────────────────────────+
+│ http://y.io/z.glb                             | AFRAME app                                             │
+│-----------------------------------------------+--------------------------------------------------------│
+│                                               |                                                        │
+│                                               | after loading the glb, john can be placed into the     │
+│     +-[3D mesh]-+                             | castle via hands, because the author added metadata to │
+│     |    / \    |                             | john via either:                                       │
+│     |   /   \   |                             |                                                        │
+│     |  /     \  |                             | 1. Blender (custom property-box, no plugins needed)    │
+│     |  |_____|  |                             |                                                        │
+│     +-----│-----+                             | 2. javascript-code:                                    │
+│           │                                   |                                                        │
+│           ├─ name: castle                     |     for( var com in this.el.components ){              │
+│           └─ tag: house baroque               |       this.el.object3D.userData[`-AFRAME-${com}`] = '' │
+│                                               |     }                                                  │
+│ [3D mesh-+                                    |     // save to z.glb in AFRAME inspector               │
+│ |        ├─ name: john                        |                                                        │
+│ |    O   ├─ age: 23                           |                                                        │
+│ |   /|\  ├─ -AFRAME-grabbable:      ''        | > inits 'grabbable' component on object john           │
+│ |   / \  ├─ -AFRAME-material.color: '#F0A'    | > inits 'material' component on object john            │
+│ |        ├─ -AFRAME-text.value:  '{name}{age}'| > inits 'text' component (*) with value 'john'         │
+│ |        ├─ -THREE-material.fog: false        | > changes material settings in THREE.js app            │
+│ |        ├─ -GODOT-Label3D.text: '{name}{age}'| > inits 'Label3D' component (*) in Godot               │
+│ +--------+                                    |                                                        │
+│                                               |                                                        │
+├─ -AFRAME-version: '1.6.0'                     | >                                                      │
+├─ -GODOT-version:  '4.3'                       | > exporters/authors can report targeted version        │
+│                                               |                                                        │
++────────────────────────────────────────────────────────────────────────────────────────────────────────+
+
+   *  key/value syntax: -<vendorname>-<component|version>.<key>
+      [string/boolean/float/int]-value
+
+   String-templatevalues are evaluated as per URI Templates (RFC6570)
+   (https://www.rfc-editor.org/rfc/rfc6570) Level 1.
+
+   |  This 'separating of mechanism from policy' (unix rule) does
+   |  *somewhat* break portability of an XR experience, but still
+   |  prevents (E-waste of) handcoded virtual worlds.  It allows for (XR
+   |  experience) metadata to survive in future 3D engines and scene-
+   |  fileformats.
+
+
+
+
+
+
+
+
+
+
+van Kammen                Expires 24 March 2025                [Page 36]
+
+Internet-Draft                XR Fragments                September 2024
+
+
+25.  Security Considerations
 
    The only dynamic parts are W3C Media Fragments
    (https://www.w3.org/TR/media-frags/) and URI Templates (RFC6570)
    (https://www.rfc-editor.org/rfc/rfc6570).
    The use of URI Templates is limited to pre-defined variables and
    Level0 fragments-expansion only, which makes it quite safe.
-   In fact, it is much safer than relying on a scripting language
+   n fact, it is much safer than relying on a scripting language
    (javascript) which can change URN too.
 
-23.  FAQ
+26.  FAQ
 
    *Q:* Why is everything HTTP GET-based, what about POST/PUT/DELETE
    HATEOS
@@ -1898,14 +2052,6 @@ Internet-Draft                XR Fragments                     July 2024
    scripting language.
    XR Fragments supports filtering objects in a scene only, because in
    the history of the javascript-powered web, showing/hiding document-
-
-
-
-van Kammen               Expires 13 January 2025               [Page 34]
-
-Internet-Draft                XR Fragments                     July 2024
-
-
    entities seems to be one of the most popular basic usecases.
    Doing advanced scripting & networkrequests under the hood are
    obviously interesting endavours, but this is something which should
@@ -1915,16 +2061,24 @@ Internet-Draft                XR Fragments                     July 2024
    place, to 'extend' experiences, in contrast to code/javascript inside
    hypermedia documents (this turned out as a hypermedia antipattern).
 
-24.  authors
+27.  authors
 
    *  Leon van Kammen (@lvk@mastodon.online)
    *  Jens Finkhäuser (@jens@social.finkhaeuser.de)
 
-25.  IANA Considerations
+
+
+
+van Kammen                Expires 24 March 2025                [Page 37]
+
+Internet-Draft                XR Fragments                September 2024
+
+
+28.  IANA Considerations
 
    This document has no IANA actions.
 
-26.  Acknowledgments
+29.  Acknowledgments
 
    *  NLNET (https://nlnet.nl)
    *  Future of Text (https://futureoftext.org)
@@ -1939,7 +2093,7 @@ Internet-Draft                XR Fragments                     July 2024
    *  Brandel Zackernuk
    *  Mark Anderson
 
-27.  Appendix: Definitions
+30.  Appendix: Definitions
 
      +=================+=============================================+
      | definition      | explanation                                 |
@@ -1954,14 +2108,6 @@ Internet-Draft                XR Fragments                     July 2024
      | 3D object       | an object inside a scene characterized by   |
      |                 | vertex-, face- and customproperty data.     |
      +-----------------+---------------------------------------------+
-
-
-
-van Kammen               Expires 13 January 2025               [Page 35]
-
-Internet-Draft                XR Fragments                     July 2024
-
-
      | URI             | some resource at something somewhere via    |
      |                 | someprotocol (http://me.com/foo.glb#foo or  |
      |                 | e76f8efec8efce98e6f see interpeer.io        |
@@ -1976,6 +2122,14 @@ Internet-Draft                XR Fragments                     July 2024
      |                 | Object(nodes), relevant to machines and a   |
      |                 | human minority (academics/developers)       |
      +-----------------+---------------------------------------------+
+
+
+
+van Kammen                Expires 24 March 2025                [Page 38]
+
+Internet-Draft                XR Fragments                September 2024
+
+
      | XR fragment     | URI Fragment with spatial hints like        |
      |                 | #pos=0,0,0&t=1,100 e.g.                     |
      +-----------------+---------------------------------------------+
@@ -2010,14 +2164,6 @@ Internet-Draft                XR Fragments                     July 2024
      |                 | indirectly visible/editable in XR.          |
      +-----------------+---------------------------------------------+
      | requestless     | metadata which never spawns new requests    |
-
-
-
-van Kammen               Expires 13 January 2025               [Page 36]
-
-Internet-Draft                XR Fragments                     July 2024
-
-
      | metadata        | (unlike RDF/HTML, which can cause           |
      |                 | framerate-dropping, hence not used a lot in |
      |                 | games)                                      |
@@ -2032,6 +2178,14 @@ Internet-Draft                XR Fragments                     July 2024
      | extrospective   | outward sensemaking ("I'm fairly sure John  |
      |                 | is a person who lives in oklahoma")         |
      +-----------------+---------------------------------------------+
+
+
+
+van Kammen                Expires 24 March 2025                [Page 39]
+
+Internet-Draft                XR Fragments                September 2024
+
+
      | ◻               | ascii representation of an 3D object/mesh   |
      +-----------------+---------------------------------------------+
      | (un)obtrusive   | obtrusive: wrapping human text/thought in   |
@@ -2052,7 +2206,7 @@ Internet-Draft                XR Fragments                     July 2024
      |                 | XML                                         |
      +-----------------+---------------------------------------------+
 
-                                  Table 14
+                                  Table 15
 
 
 
@@ -2069,4 +2223,18 @@ Internet-Draft                XR Fragments                     July 2024
 
 
 
-van Kammen               Expires 13 January 2025               [Page 37]
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+van Kammen                Expires 24 March 2025                [Page 40]
diff --git a/doc/RFC_XR_Fragments.xml b/doc/RFC_XR_Fragments.xml
index d025a23..d5490ee 100644
--- a/doc/RFC_XR_Fragments.xml
+++ b/doc/RFC_XR_Fragments.xml
@@ -10,7 +10,7 @@
 <workgroup>Jens &amp; Leon Internet Engineering Task Force</workgroup>
 
 <abstract>
-<t>This draft is a specification for 4D URI's &amp; <eref target="https://github.com/coderofsalvation/hypermediatic">hypermediatic</eref> navigation, to enable a spatial web for hypermedia browsers with- or without a network-connection.<br />
+<t>This draft is a specification for interactive URI-controllable 3D files, enabling <eref target="https://github.com/coderofsalvation/hypermediatic">hypermediatic</eref> navigation, to enable a spatial web for hypermedia browsers with- or without a network-connection.<br />
 
 The specification uses <eref target="https://www.w3.org/TR/media-frags/">W3C Media Fragments</eref> and <eref target="https://www.rfc-editor.org/rfc/rfc6570">URI Templates (RFC6570)</eref> to promote spatial addressibility, sharing, navigation, filtering and databinding objects for (XR) Browsers.<br />
 
@@ -1134,99 +1134,105 @@ The XR Fragment-compatible browser can let the enduser access visual-meta(data)-
 <section anchor="reflection-mapping"><name>Reflection Mapping</name>
 <t>Environment mapping is crucial for creating realistic reflections and lighting effects on 3D objects.
 To apply environment mapping efficiently in a 3D scene, traverse the scene graph and assign each object's environment map based on the nearest ancestor's texture map. This ensures that objects inherit the correct environment mapping from their closest parent with a texture, enhancing the visual consistency and realism.</t>
-<t>``````
-  +--------------------------------+<br />
-  |                                |<br />
-  |  index.usdz                    |<br />
-  |    │                           |<br />
-  |    └── ◻ sphere (texture:foo)  |
-  |        └ ◻ cube (texture:bar)  | envMap = foo
+
+<artwork><![CDATA[  +--------------------------------+  
+  |                                |  
+  |  index.usdz                    |  
+  |    │                           |  
+  |    └── ◻ sphere (texture:foo)  | 
+  |        └ ◻ cube (texture:bar)  | envMap = foo 
   |         └ ◻ cylinder           | envMap = bar
-  +--------------------------------+</t>
-
-<artwork><![CDATA[
-Most 3D viewers apply one and the same environment map for various models, however this logic 
-allows a more natural & automatic strategy for reflection mapping. 
-
-# Transclusion (broken link) resolution
-
-In spirit of Ted Nelson's 'transclusion resolution', there's a soft-mechanism to harden links & minimize broken links in various ways:
-
-1. defining a different transport protocol (https vs ipfs or DAT) in `src` or `href` values can make a difference
-2. mirroring files on another protocol using (HTTP) errorcode tags in `src` or `href` properties
-3. in case of `src`: nesting a copy of the embedded object in the placeholder object (`embeddedObject`) will not be replaced when the request fails
-
-> due to the popularity, maturity and extensiveness of HTTP codes for client/server communication, non-HTTP protocols easily map to HTTP codes (ipfs ERR_NOT_FOUND maps to 404 e.g.)
-
-For example:
-
+  +--------------------------------+
 ]]>
 </artwork>
-<t>+────────────────────────────────────────────────────────+
+<t>Most 3D viewers apply one and the same environment map for various models, however this logic
+allows a more natural &amp; automatic strategy for reflection mapping.</t>
+</section>
+
+<section anchor="transclusion-broken-link-resolution"><name>Transclusion (broken link) resolution</name>
+<t>In spirit of Ted Nelson's 'transclusion resolution', there's a soft-mechanism to harden links &amp; minimize broken links in various ways:</t>
+
+<ol spacing="compact">
+<li>defining a different transport protocol (https vs ipfs or DAT) in <tt>src</tt> or <tt>href</tt> values can make a difference</li>
+<li>mirroring files on another protocol using (HTTP) errorcode tags in <tt>src</tt> or <tt>href</tt> properties</li>
+<li>in case of <tt>src</tt>: nesting a copy of the embedded object in the placeholder object (<tt>embeddedObject</tt>) will not be replaced when the request fails</li>
+</ol>
+<blockquote><t>due to the popularity, maturity and extensiveness of HTTP codes for client/server communication, non-HTTP protocols easily map to HTTP codes (ipfs ERR_NOT_FOUND maps to 404 e.g.)</t>
+</blockquote><t>For example:</t>
+
+<artwork><![CDATA[  +────────────────────────────────────────────────────────+ 
   │                                                        │
   │  index.gltf                                            │
   │    │                                                   │
   │    │ #: #-offlinetext                                  │
   │    │                                                   │
   │    ├── ◻ buttonA                                       │
-  │    │      └ href:     <eref target="http://foo.io/campagne.fbx">http://foo.io/campagne.fbx</eref>       │
+  │    │      └ href:     http://foo.io/campagne.fbx       │
   │    │      └ href@404: ipfs://foo.io/campagne.fbx       │
   │    │      └ href@400: #clienterrortext                 │
   │    │      └ ◻ offlinetext                              │
   │    │                                                   │
-  │    └── ◻ embeddedObject                          &lt;--------- the meshdata inside embeddedObject will (not)
-  │           └ src: <eref target="https://foo.io/bar.gltf">https://foo.io/bar.gltf</eref>               │    be flushed when the request (does not) succeed.
-  │           └ src@404: <eref target="http://foo.io/bar.gltf">http://foo.io/bar.gltf</eref>            │    So worstcase the 3D data (of the time of publishing index.gltf)
-  │           └ src@400: <eref target="https://archive.org/l2kj43.gltf">https://archive.org/l2kj43.gltf</eref>   │    will be displayed.
+  │    └── ◻ embeddedObject                          <--------- the meshdata inside embeddedObject will (not)
+  │           └ src: https://foo.io/bar.gltf               │    be flushed when the request (does not) succeed.
+  │           └ src@404: http://foo.io/bar.gltf            │    So worstcase the 3D data (of the time of publishing index.gltf)
+  │           └ src@400: https://archive.org/l2kj43.gltf   │    will be displayed.
   │                                                        │
-  +────────────────────────────────────────────────────────+</t>
-
-<artwork><![CDATA[
-# Topic-based index-less Webrings 
-
-As hashtags in URLs map to the XWRG, `href`-values can be used to promote topic-based index-less webrings.<br>
-Consider 3D scenes linking to eachother using these `href` values:
-
-* `href: schoolA.edu/projects.gltf#math`
-* `href: schoolB.edu/projects.gltf#math`
-* `href: university.edu/projects.gltf#math`
-
-These links would all show visible links to math-tagged objects in the scene.<br>
-To filter out non-related objects one could take it a step further using filters:
-
-* `href: schoolA.edu/projects.gltf#math&-topics math`
-* `href: schoolB.edu/projects.gltf#math&-courses math`
-* `href: university.edu/projects.gltf#math&-theme math`
-
-> This would hide all object tagged with `topic`, `courses` or `theme` (including math) so that later only objects tagged with `math` will be visible 
-
-This makes spatial content multi-purpose, without the need to separate content into separate files, or show/hide things using a complex logiclayer like javascript.
-
-# URI Templates (RFC6570)
-
-XR Fragments adopts Level1 URI **Fragment** expansion to provide safe interactivity.<br>
-The following demonstrates a simple video player:
+  +────────────────────────────────────────────────────────+
 
 ]]>
 </artwork>
-<t>+─────────────────────────────────────────────+
+</section>
+
+<section anchor="topic-based-index-less-webrings"><name>Topic-based index-less Webrings</name>
+<t>As hashtags in URLs map to the XWRG, <tt>href</tt>-values can be used to promote topic-based index-less webrings.<br />
+
+Consider 3D scenes linking to eachother using these <tt>href</tt> values:</t>
+
+<ul spacing="compact">
+<li><tt>href: schoolA.edu/projects.gltf#math</tt></li>
+<li><tt>href: schoolB.edu/projects.gltf#math</tt></li>
+<li><tt>href: university.edu/projects.gltf#math</tt></li>
+</ul>
+<t>These links would all show visible links to math-tagged objects in the scene.<br />
+
+To filter out non-related objects one could take it a step further using filters:</t>
+
+<ul spacing="compact">
+<li><tt>href: schoolA.edu/projects.gltf#math&amp;-topics math</tt></li>
+<li><tt>href: schoolB.edu/projects.gltf#math&amp;-courses math</tt></li>
+<li><tt>href: university.edu/projects.gltf#math&amp;-theme math</tt></li>
+</ul>
+<blockquote><t>This would hide all object tagged with <tt>topic</tt>, <tt>courses</tt> or <tt>theme</tt> (including math) so that later only objects tagged with <tt>math</tt> will be visible</t>
+</blockquote><t>This makes spatial content multi-purpose, without the need to separate content into separate files, or show/hide things using a complex logiclayer like javascript.</t>
+</section>
+
+<section anchor="uri-templates-rfc6570"><name>URI Templates (RFC6570)</name>
+<t>XR Fragments adopts Level1 URI <strong>Fragment</strong> expansion to provide safe interactivity.<br />
+
+The following demonstrates a simple video player:</t>
+
+<artwork><![CDATA[
+  +─────────────────────────────────────────────+
   │                                             │
-  │   foo.usdz                                  │<br />
-  │     │                                       │<br />
-  │     │                                       │<br />
+  │   foo.usdz                                  │          
+  │     │                                       │          
+  │     │                                       │          
   │     ├── ◻ stopbutton                        │
   │     │      ├ #:    #-stopbutton             │
-  │     │      └ href: #player=stop&amp;-stopbutton │  (stop and hide stop-button)
-  │     │                                       │<br />
+  │     │      └ href: #player=stop&-stopbutton │  (stop and hide stop-button)
+  │     │                                       │          
   │     └── ◻ plane                             │
   │            ├ play: #t=l:0,10                │
   │            ├ stop: #t=0,0                   │
-  │            ├ href: #player=play&amp;stopbutton  │  (play and show stop-button)
+  │            ├ href: #player=play&stopbutton  │  (play and show stop-button)
   │            └ src:  cat.mp4#{player}         │
   │                                             │
   │                                             │
-  +─────────────────────────────────────────────+</t>
-<t>```</t>
+  +─────────────────────────────────────────────+
+
+
+]]>
+</artwork>
 </section>
 
 <section anchor="additional-scene-metadata"><name>Additional scene metadata</name>
@@ -1339,6 +1345,76 @@ Therefore a 2-button navigation-interface is the bare minimum interface:</t>
 <li>the TTS reads the href-value (and/or aria-description if available)</li>
 </ol>
 </section>
+
+<section anchor="xr-fragment-vendor-prefixes"><name>XR Fragment Vendor Prefixes</name>
+<t>Vendor Prefixes (XRFVP's) allows embedding a 3D file with popular 3D engines/framework-specific features via metadata:</t>
+<table>
+<thead>
+<tr>
+<th>what</th>
+<th>XR metadata</th>
+<th>Lowest common denominator</th>
+</tr>
+</thead>
+
+<tbody>
+<tr>
+<td>XR Fragments</td>
+<td>vendor-agnostic</td>
+<td>camera + 3D object(file) load/embed/click/referencing</td>
+</tr>
+
+<tr>
+<td>XR Fragments VP's</td>
+<td>vendor-<strong>specific</strong></td>
+<td>Entity-Component System (ECS)</td>
+</tr>
+</tbody>
+</table><t>Vendor-specific metadata in a 3D scenefiles, are similar to vendor-specific <eref target="https://en.wikipedia.org/wiki/CSS#Vendor_prefixes">CSS-prefixes</eref> (<tt>-moz-opacity: 0.2</tt> e.g.).
+This allows popular 3D engines/frameworks, to initialize specific features when loading a scene/object, in a progressive enhanced way.</t>
+<blockquote><t>Why? Because not all XR interactions can be solved/standardized by embedding XR Fragments into any 3D file.
+Some XR experiences need more than <strong>navigation</strong> and <strong>show/hide/filtering</strong> of objects (via click-state machines).
+The lowest common denominator between s that 3D engines use entity-component-system</t>
+</blockquote><t>For example, the following metadata can be added to a .glb file, to make an object grabbable in AFRAME:</t>
+
+<artwork><![CDATA[+────────────────────────────────────────────────────────────────────────────────────────────────────────+ 
+│ http://y.io/z.glb                             | AFRAME app                                             │ 
+│-----------------------------------------------+--------------------------------------------------------│ 
+│                                               |                                                        │
+│                                               | after loading the glb, john can be placed into the     │ 
+│     +-[3D mesh]-+                             | castle via hands, because the author added metadata to │  
+│     |    / \    |                             | john via either:                                       │  
+│     |   /   \   |                             |                                                        │ 
+│     |  /     \  |                             | 1. Blender (custom property-box, no plugins needed)    │ 
+│     |  |_____|  |                             |                                                        │  
+│     +-----│-----+                             | 2. javascript-code:                                    │  
+│           │                                   |                                                        │  
+│           ├─ name: castle                     |     for( var com in this.el.components ){              │  
+│           └─ tag: house baroque               |       this.el.object3D.userData[`-AFRAME-${com}`] = '' │  
+│                                               |     }                                                  │  
+│ [3D mesh-+                                    |     // save to z.glb in AFRAME inspector               │ 
+│ |        ├─ name: john                        |                                                        │  
+│ |    O   ├─ age: 23                           |                                                        │  
+│ |   /|\  ├─ -AFRAME-grabbable:      ''        | > inits 'grabbable' component on object john           │ 
+│ |   / \  ├─ -AFRAME-material.color: '#F0A'    | > inits 'material' component on object john            │  
+│ |        ├─ -AFRAME-text.value:  '{name}{age}'| > inits 'text' component (*) with value 'john'         │  
+│ |        ├─ -THREE-material.fog: false        | > changes material settings in THREE.js app            │ 
+│ |        ├─ -GODOT-Label3D.text: '{name}{age}'| > inits 'Label3D' component (*) in Godot               │  
+│ +--------+                                    |                                                        │
+│                                               |                                                        │
+├─ -AFRAME-version: '1.6.0'                     | >                                                      │
+├─ -GODOT-version:  '4.3'                       | > exporters/authors can report targeted version        │
+│                                               |                                                        │
++────────────────────────────────────────────────────────────────────────────────────────────────────────+ 
+]]>
+</artwork>
+
+<ul spacing="compact">
+<li>key/value syntax: -<tt>&lt;vendorname&gt;</tt>-<tt>&lt;component|version&gt;</tt>.<tt>&lt;key&gt;</tt>  <tt>[string/boolean/float/int]</tt>-value</li>
+</ul>
+<t>String-templatevalues are evaluated as per <eref target="https://www.rfc-editor.org/rfc/rfc6570">URI Templates (RFC6570)</eref> Level 1.</t>
+<blockquote><t>This 'separating of mechanism from policy' (unix rule) does <strong>somewhat</strong> break portability of an XR experience, but still prevents (E-waste of) handcoded virtual worlds. It allows for (XR experience) metadata to survive in future 3D engines and scene-fileformats.</t>
+</blockquote></section>
 </section>
 
 <section anchor="security-considerations"><name>Security Considerations</name>
@@ -1346,7 +1422,7 @@ Therefore a 2-button navigation-interface is the bare minimum interface:</t>
 
 The use of URI Templates is limited to pre-defined variables and Level0 fragments-expansion only, which makes it quite safe.<br />
 
-In fact, it is much safer than relying on a scripting language (javascript) which can change URN too.</t>
+n fact, it is much safer than relying on a scripting language (javascript) which can change URN too.</t>
 </section>
 
 <section anchor="faq"><name>FAQ</name>