xrfragment/doc/RFC_XR_Fragments.txt

Internet Engineering Task Force                          L.R. van Kammen
Internet-Draft                                          7 September 2023
Intended status: Informational                                          



                              XR Fragments
                   draft-XRFRAGMENTS-leonvankammen-00

Abstract

   This draft offers a specification for 4D URLs & navigation, to link
   3D scenes and text together with- or without a network-connection.
   The specification promotes spatial addressibility, sharing,
   navigation, query-ing and tagging interactive (text)objects across
   for (XR) Browsers.
   XR Fragments allows us to enrich existing dataformats, by recursive
   use of existing proven technologies like URI Fragments
   (https://en.wikipedia.org/wiki/URI_fragment) and BibTags notation.

   Almost every idea in this document is demonstrated at
   https://xrfragment.org (https://xrfragment.org)

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 10 March 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.



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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Core principle  . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   4.  List of URI Fragments . . . . . . . . . . . . . . . . . . . .   3
   5.  List of metadata for 3D nodes . . . . . . . . . . . . . . . .   4
   6.  Navigating 3D . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Embedding 3D content  . . . . . . . . . . . . . . . . . . . .   5
   8.  XR Fragment queries . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  including/excluding . . . . . . . . . . . . . . . . . . .   6
     8.2.  Query Parser  . . . . . . . . . . . . . . . . . . . . . .   7
     8.3.  XR Fragment URI Grammar . . . . . . . . . . . . . . . . .   7
   9.  Text in XR (tagging,linking to spatial objects) . . . . . . .   8
     9.1.  Default Data URI mimetype . . . . . . . . . . . . . . . .  11
     9.2.  URL and Data URI  . . . . . . . . . . . . . . . . . . . .  12
     9.3.  Bibs & BibTeX: lowest common denominator for linking
           data  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.4.  XR Text example parser  . . . . . . . . . . . . . . . . .  15
   10. HYPER copy/paste  . . . . . . . . . . . . . . . . . . . . . .  17
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  17
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   14. Appendix: Definitions . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   How can we add more features to existing text & 3D scenes, without
   introducing new dataformats?
   Historically, there's many attempts to create the ultimate
   markuplanguage or 3D fileformat.
   Their lowest common denominator is: (co)authoring using plain text.
   XR Fragments allows us to enrich/connect existing dataformats, by
   recursive use of existing technologies:

   1.  addressibility and navigation of 3D scenes/objects: URI Fragments
       (https://en.wikipedia.org/wiki/URI_fragment) + src/href spatial
       metadata
   2.  hasslefree tagging across text and spatial objects using bibs
       (https://github.com/coderofsalvation/tagbibs) / BibTags
       (https://en.wikipedia.org/wiki/BibTeX) as appendix (see visual-
       meta (https://visual-meta.info) e.g.)



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   |  NOTE: The chapters in this document are ordered from highlevel to
   |  lowlevel (technical) as much as possible

2.  Core principle

   XR Fragments strives to serve (nontechnical/fuzzy) humans first, and
   machine(implementations) later, by ensuring hasslefree text-vs-
   thought feedback loops.
   This also means that the repair-ability of machine-matters should be
   human friendly too (not too complex).

   |  "When a car breaks down, the ones *without* turbosupercharger are
   |  easier to fix"

   Let's always focus on average humans: our fuzzy symbolical mind must
   be served first, before serving a greater categorized typesafe RDF
   hive mind (https://en.wikipedia.org/wiki/Borg)).

   |  Humans first, machines (AI) later.

   Thererfore, XR Fragments does not look at XR (or the web) thru the
   lens of HTML.
   XR Fragments itself is HTML-agnostic, though pseudo-XR Fragment
   browsers *can* be implemented on top of HTML/Javascript.

3.  Conventions and Definitions

   See appendix below in case certain terms are not clear.

4.  List of URI Fragments

    +==========+=========+==============+============================+
    | fragment | type    | example      | info                       |
    +==========+=========+==============+============================+
    | #pos     | vector3 | #pos=0.5,0,0 | positions camera to xyz-   |
    |          |         |              | coord 0.5,0,0              |
    +----------+---------+--------------+----------------------------+
    | #rot     | vector3 | #rot=0,90,0  | rotates camera to xyz-     |
    |          |         |              | coord 0.5,0,0              |
    +----------+---------+--------------+----------------------------+
    | #t       | vector2 | #t=500,1000  | sets animation-loop range  |
    |          |         |              | between frame 500 and 1000 |
    +----------+---------+--------------+----------------------------+
    | #......  | string  | #.cubes      | object(s) of interest      |
    |          |         | #cube        | (fragment to object name   |
    |          |         |              | or class mapping)          |
    +----------+---------+--------------+----------------------------+




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                                 Table 1

   |  xyz coordinates are similar to ones found in SVG Media Fragments

5.  List of metadata for 3D nodes

     +=======+========+================+============================+
     | key   | type   | example (JSON) | info                       |
     +=======+========+================+============================+
     | name  | string | "name": "cube" | available in all 3D        |
     |       |        |                | fileformats & scenes       |
     +-------+--------+----------------+----------------------------+
     | class | string | "class":       | available through custom   |
     |       |        | "cubes"        | property in 3D fileformats |
     +-------+--------+----------------+----------------------------+
     | href  | string | "href":        | available through custom   |
     |       |        | "b.gltf"       | property in 3D fileformats |
     +-------+--------+----------------+----------------------------+
     | src   | string | "src":         | available through custom   |
     |       |        | "#q=cube"      | property in 3D fileformats |
     +-------+--------+----------------+----------------------------+

                                 Table 2

   Popular compatible 3D fileformats: .gltf, .obj, .fbx, .usdz, .json
   (THREE.js), .dae and so on.

   |  NOTE: XR Fragments are file-agnostic, which means that the
   |  metadata exist in programmatic 3D scene(nodes) too.

6.  Navigating 3D

   Here's an ascii representation of a 3D scene-graph which contains 3D
   objects ◻ and their metadata:

  +--------------------------------------------------------+
  |                                                        |
  |  index.gltf                                            |
  |    │                                                   |
  |    ├── ◻ buttonA                                       |
  |    │      └ href: #pos=1,0,1&t=100,200                 |
  |    │                                                   |
  |    └── ◻ buttonB                                       |
  |           └ href: other.fbx                            |   <-- file-agnostic (can be .gltf .obj etc)
  |                                                        |
  +--------------------------------------------------------+





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   An XR Fragment-compatible browser viewing this scene, allows the end-
   user to interact with the buttonA and buttonB.
   In case of buttonA the end-user will be teleported to another
   location and time in the *current loaded scene*, but buttonB will
   *replace the current scene* with a new one, like other.fbx.

7.  Embedding 3D content

   Here's an ascii representation of a 3D scene-graph with 3D objects
   &#9723; which embeds remote & local 3D objects &#9723; (without)
   using queries:

  +--------------------------------------------------------+  +-------------------------+
  |                                                        |  |                         |
  |  index.gltf                                            |  | ocean.com/aquarium.fbx  |
  |    │                                                   |  |   │                     |
  |    ├── ◻ canvas                                        |  |   └── ◻ fishbowl        |
  |    │      └ src: painting.png                          |  |         ├─ ◻ bass       |
  |    │                                                   |  |         └─ ◻ tuna       |
  |    ├── ◻ aquariumcube                                  |  |                         |
  |    │      └ src: ://rescue.com/fish.gltf#q=bass%20tuna |  +-------------------------+
  |    │                                                   |
  |    ├── ◻ bedroom                                       |
  |    │      └ src: #q=canvas                             |
  |    │                                                   |
  |    └── ◻ livingroom                                    |
  |           └ src: #q=canvas                             |
  |                                                        |
  +--------------------------------------------------------+

   An XR Fragment-compatible browser viewing this scene, lazy-loads and
   projects painting.png onto the (plane) object called canvas (which is
   copy-instanced in the bed and livingroom).
   Also, after lazy-loading ocean.com/aquarium.gltf, only the queried
   objects bass and tuna will be instanced inside aquariumcube.
   Resizing will be happen accordingly to its placeholder object
   aquariumcube, see chapter Scaling.

8.  XR Fragment queries

   Include, exclude, hide/shows objects using space-separated strings:

   *  #q=cube
   *  #q=cube -ball_inside_cube
   *  #q=* -sky
   *  #q=-.language .english
   *  #q=cube&rot=0,90,0
   *  #q=price:>2 price:<5



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   It's simple but powerful syntax which allows <b>css</b>-like class/
   id-selectors with a searchengine prompt-style feeling:

   1.  queries are showing/hiding objects *only* when defined as src
       value (prevents sharing of scene-tampered URL's).
   2.  queries are highlighting objects when defined in the top-Level
       (browser) URL (bar).
   3.  search words like cube and foo in #q=cube foo are matched against
       3D object names or custom metadata-key(values)
   4.  search words like cube and foo in #q=cube foo are matched against
       tags (BibTeX) inside plaintext src values like @cube{redcube, ...
       e.g.
   5.  # equals #q=*
   6.  words starting with . like .german match class-metadata of 3D
       objects like "class":"german"
   7.  words starting with . like .german match class-metadata of
       (BibTeX) tags in XR Text objects like @german{KarlHeinz, ... e.g.

   |  *For example*: #q=.foo is a shorthand for #q=class:foo, which will
   |  select objects with custom property class:foo.  Just a simple
   |  #q=cube will simply select an object named cube.

   *  see an example video here
      (https://coderofsalvation.github.io/xrfragment.media/queries.mp4)

8.1.  including/excluding

      +==========+=================================================+
      | operator | info                                            |
      +==========+=================================================+
      | *        | select all objects (only useful in src custom   |
      |          | property)                                       |
      +----------+-------------------------------------------------+
      | -        | removes/hides object(s)                         |
      +----------+-------------------------------------------------+
      | :        | indicates an object-embedded custom property    |
      |          | key/value                                       |
      +----------+-------------------------------------------------+
      | .        | alias for "class" :".foo" equals class:foo      |
      +----------+-------------------------------------------------+
      | > <      | compare float or int number                     |
      +----------+-------------------------------------------------+
      | /        | reference to root-scene.                        |
      |          | Useful in case of (preventing) showing/hiding   |
      |          | objects in nested scenes (instanced by src) (*) |
      +----------+-------------------------------------------------+

                                 Table 3



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   |  * = #q=-/cube hides object cube only in the root-scene (not nested
   |  cube objects)
   |  #q=-cube hides both object cube in the root-scene <b>AND</b>
   |  nested skybox objects |

   &#187; example implementation
   (https://github.com/coderofsalvation/xrfragment/blob/main/src/3rd/js/
   three/xrf/q.js) &#187; example 3D asset
   (https://github.com/coderofsalvation/xrfragment/blob/main/example/
   assets/query.gltf#L192) &#187; discussion
   (https://github.com/coderofsalvation/xrfragment/issues/3)

8.2.  Query Parser

   Here's how to write a query parser:

   1.   create an associative array/object to store query-arguments as
        objects
   2.   detect object id's & properties foo:1 and foo (reference regex:
        /^.*:[><=!]?/ )
   3.   detect excluders like -foo,-foo:1,-.foo,-/foo (reference regex:
        /^-/ )
   4.   detect root selectors like /foo (reference regex: /^[-]?\// )
   5.   detect class selectors like .foo (reference regex: /^[-]?class$/
        )
   6.   detect number values like foo:1 (reference regex: /^[0-9\.]+$/ )
   7.   expand aliases like .foo into class:foo
   8.   for every query token split string on :
   9.   create an empty array rules
   10.  then strip key-operator: convert "-foo" into "foo"
   11.  add operator and value to rule-array
   12.  therefore we we set id to true or false (false=excluder -)
   13.  and we set root to true or false (true=/ root selector is
        present)
   14.  we convert key '/foo' into 'foo'
   15.  finally we add the key/value to the store like store.foo =
        {id:false,root:true} e.g.

   |  An example query-parser (which compiles to many languages) can be
   |  found here
   |  (https://github.com/coderofsalvation/xrfragment/blob/main/src/
   |  xrfragment/Query.hx)

8.3.  XR Fragment URI Grammar

   reserved    = gen-delims / sub-delims
   gen-delims  = "#" / "&"
   sub-delims  = "," / "="



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   |  Example: ://foo.com/my3d.gltf#pos=1,0,0&prio=-5&t=0,100

     +=============================+=================================+
     | Demo                        | Explanation                     |
     +=============================+=================================+
     | pos=1,2,3                   | vector/coordinate argument e.g. |
     +-----------------------------+---------------------------------+
     | pos=1,2,3&rot=0,90,0&q=.foo | combinators                     |
     +-----------------------------+---------------------------------+

                                  Table 4

9.  Text in XR (tagging,linking to spatial objects)

   We still think and speak in simple text, not in HTML or RDF.
   The most advanced human will probably not shout <h1>FIRE!</h1> in
   case of emergency.
   Given the new dawn of (non-keyboard) XR interfaces, keeping text as
   is (not obscuring with markup) is preferred.
   Ideally metadata must come *later with* text, but not *obfuscate* the
   text, or *in another* file.

   |  Humans first, machines (AI) later (core principle (#core-
   |  principle)

   This way:

   1.  XR Fragments allows <b id="tagging-text">hasslefree XR text
       tagging</b>, using BibTeX metadata *at the end of content* (like
       visual-meta (https://visual.meta.info)).
   2.  XR Fragments allows hasslefree <a href="#textual-tag">textual
       tagging</a>, <a href="#spatial-tag">spatial tagging</a>, and <a
       href="#supra-tagging">supra tagging</a>, by mapping 3D/text
       object (class)names using BibTeX 'tags'
   3.  Bibs/BibTeX-appendices is first-choice *requestless metadata*-
       layer for XR text, HTML/RDF/JSON is great (but fits better in the
       application-layer)
   4.  Default font (unless specified otherwise) is a modern monospace
       font, for maximized tabular expressiveness (see the core
       principle (#core-principle)).
   5.  anti-pattern: hardcoupling a mandatory *obtrusive markuplanguage*
       or framework with an XR browsers (HTML/VRML/Javascript) (see the
       core principle (#core-principle))
   6.  anti-pattern: limiting human introspection, by immediately
       funneling human thought into typesafe, precise, pre-categorized
       metadata like RDF (see the core principle (#core-principle))





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   This allows recursive connections between text itself, as well as 3D
   objects and vice versa, using *BibTags* :

  +---------------------------------------------+         +------------------+
  | My Notes                                    |         |        / \       |
  |                                             |         |       /   \      |
  | The houses here are built in baroque style. |         |      /house\     |
  |                                             |         |      |_____|     |
  |                                             |         +---------|--------+
  | @house{houses,                              >----'house'--------|    class/name match?
  |   url  = {#.house}                          >----'houses'-------`    class/name match?
  | }                                           |
  +---------------------------------------------+

   This allows instant realtime tagging of objects at various scopes:




































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   +====================================+=============================+
   | scope                              | matching algo               |
   +====================================+=============================+
   | <b id="textual-                    | text containing 'houses' is |
   | tagging">textual</b>               | now automatically tagged    |
   |                                    | with 'house' (incl.         |
   |                                    | plaintext src child nodes)  |
   +------------------------------------+-----------------------------+
   | <b id="spatial-                    | spatial object(s) with      |
   | tagging">spatial</b>               | "class":"house" (because of |
   |                                    | {#.house}) are now          |
   |                                    | automatically tagged with   |
   |                                    | 'house' (incl. child nodes) |
   +------------------------------------+-----------------------------+
   | <b id="supra-tagging">supra</b>    | text- or spatial-object(s)  |
   |                                    | (non-descendant nodes)      |
   |                                    | elsewhere, named 'house',   |
   |                                    | are automatically tagged    |
   |                                    | with 'house' (current node  |
   |                                    | to root node)               |
   +------------------------------------+-----------------------------+
   | <b id="omni-tagging">omni</b>      | text- or spatial-object(s)  |
   |                                    | (non-descendant nodes)      |
   |                                    | elsewhere, containing       |
   |                                    | class/name 'house', are     |
   |                                    | automatically tagged with   |
   |                                    | 'house' (too node to all    |
   |                                    | nodes)                      |
   +------------------------------------+-----------------------------+
   | <b id="infinite-                   | text- or spatial-object(s)  |
   | tagging">infinite</b>              | (non-descendant nodes)      |
   |                                    | elsewhere, containing       |
   |                                    | class/name 'house' or       |
   |                                    | 'houses', are automatically |
   |                                    | tagged with 'house' (too    |
   |                                    | node to all nodes)          |
   +------------------------------------+-----------------------------+

                                 Table 5

   This empowers the enduser spatial expressiveness (see the core
   principle (#core-principle)): spatial wires can be rendered, words
   can be highlighted, spatial objects can be highlighted/moved/scaled,
   links can be manipulated by the user.
   The simplicity of appending BibTeX 'tags' (humans first, machines
   later) is also demonstrated by visual-meta (https://visual-meta.info)
   in greater detail.




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   1.  The XR Browser needs to adjust tag-scope based on the endusers
       needs/focus (infinite tagging only makes sense when environment
       is scaled down significantly)
   2.  The XR Browser should always allow the human to view/edit the
       metadata, by clicking 'toggle metadata' on the 'back'
       (contextmenu e.g.) of any XR text, anywhere anytime.

   |  NOTE: infinite matches both 'house' and 'houses' in text, as well
   |  as spatial objects with "class":"house" or name "house".  This
   |  multiplexing of id/category is deliberate because of the core
   |  principle (#core-principle).

9.1.  Default Data URI mimetype

   The src-values work as expected (respecting mime-types), however:

   The XR Fragment specification bumps the traditional default browser-
   mimetype

   text/plain;charset=US-ASCII

   to a green eco-friendly:

   text/plain;charset=utf-8;bib=^@

   This indicates that bibs (https://github.com/coderofsalvation/
   tagbibs) and bibtags (https://en.wikipedia.org/wiki/BibTeX) matching
   regex ^@ will automatically get filtered out, in order to:

   *  automatically detect links between textual/spatial objects
   *  detect opiniated bibtag appendices (visual-meta (https://visual-
      meta.info) e.g.)

   It's concept is similar to literate programming, which empower local/
   remote responses to:

   *  (de)multiplex human text and metadata in one go (see the core
      principle (#core-principle))
   *  no network-overhead for metadata (see the core principle (#core-
      principle))
   *  ensuring high FPS: HTML/RDF historically is too 'requesty'/'parsy'
      for game studios
   *  rich send/receive/copy-paste everywhere by default, metadata being
      retained (see the core principle (#core-principle))
   *  netto result: less webservices, therefore less servers, and
      overall better FPS in XR





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   |  This significantly expands expressiveness and portability of human
   |  tagged text, by *postponing machine-concerns to the end of the
   |  human text* in contrast to literal interweaving of content and
   |  markupsymbols (or extra network requests, webservices e.g.).

   For all other purposes, regular mimetypes can be used (but are not
   required by the spec).
   To keep XR Fragments a lightweight spec, BibTeX is used for text/
   spatial tagging (not a scripting language or RDF e.g.).

   |  Applications are also free to attach any JSON(LD / RDF) to spatial
   |  objects using custom properties (but is not interpreted by this
   |  spec).

9.2.  URL and Data URI

  +--------------------------------------------------------------+  +------------------------+
  |                                                              |  | author.com/article.txt |
  |  index.gltf                                                  |  +------------------------+
  |    │                                                         |  |                        |
  |    ├── ◻ article_canvas                                      |  | Hello friends.         |
  |    │    └ src: ://author.com/article.txt                     |  |                        |
  |    │                                                         |  | @friend{friends        |
  |    └── ◻ note_canvas                                         |  |   ...                  |
  |           └ src:`data:welcome human\n@...`                   |  | }                      |
  |                                                              |  +------------------------+
  |                                                              |
  +--------------------------------------------------------------+

   The enduser will only see welcome human and Hello friends rendered
   spatially.  The beauty is that text (AND visual-meta) in Data URI
   promotes rich copy-paste.  In both cases, the text gets rendered
   immediately (onto a plane geometry, hence the name '_canvas').  The
   XR Fragment-compatible browser can let the enduser access visual-
   meta(data)-fields after interacting with the object (contextmenu
   e.g.).

   |  additional tagging using bibs
   |  (https://github.com/coderofsalvation/tagbibs): to tag spatial
   |  object note_canvas with 'todo', the enduser can type or speak
   |  @note_canvas@todo

   The mapping between 3D objects and text (src-data) is simple (the :

   Example:






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  +------------------------------------------------+
  |                                                |
  |  index.gltf                                    |
  |    │                                           |
  |    └── ◻ rentalhouse                           |
  |           └ class: house              <----------------- matches -------+
  |           └ ◻ note                             |                        |
  |                 └ src:`data: todo: call owner  |       bib              |
  |                              @owner@house@todo | ----> expands to     @house{owner,
  |                                                |          bibtex:     }
  |                        `                       |                      @contact{
  +------------------------------------------------+                      }

   Bi-directional mapping between 3D object names and/or classnames and
   text using bibs,BibTags & XR Fragments, allows for rich interlinking
   between text and 3D objects:

   1.  When the user surfs to https://.../index.gltf#rentalhouse the XR
       Fragments-parser points the enduser to the rentalhouse object,
       and can show contextual info about it.
   2.  When (partial) remote content is embedded thru XR Fragment
       queries (see XR Fragment queries), indirectly related metadata
       can be embedded along.

9.3.  Bibs & BibTeX: lowest common denominator for linking data

   |  "When a car breaks down, the ones *without* turbosupercharger are
   |  easier to fix"

   Unlike XML or JSON, the typeless, unnested, everything-is-text nature
   of BibTeX tags is a great advantage for introspection.
   It's a missing sensemaking precursor to extrospective RDF.
   BibTeX-appendices are already used in the digital AND physical world
   (academic books, visual-meta (https://visual-meta.info)), perhaps due
   to its terseness & simplicity.
   In that sense, it's one step up from the .ini fileformat (which has
   never leaked into the physical world like BibTex):

   1.  <b id="frictionless-copy-paste">frictionless copy/pasting</b> (by
       humans) of (unobtrusive) content AND metadata
   2.  an introspective 'sketchpad' for metadata, which can (optionally)
       mature into RDF later









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   +================+=====================================+===============+
   |characteristic  |UTF8 Plain Text (with BibTeX)        |RDF            |
   +================+=====================================+===============+
   |perspective     |introspective                        |extrospective  |
   +----------------+-------------------------------------+---------------+
   |structure       |fuzzy (sensemaking)                  |precise        |
   +----------------+-------------------------------------+---------------+
   |space/scope     |local                                |world          |
   +----------------+-------------------------------------+---------------+
   |everything is   |yes                                  |no             |
   |text (string)   |                                     |               |
   +----------------+-------------------------------------+---------------+
   |voice/paper-    |bibs                                 |no             |
   |friendly        |(https://github.com/coderofsalvation/|               |
   |                |tagbibs)                             |               |
   +----------------+-------------------------------------+---------------+
   |leaves          |yes                                  |no             |
   |(dictated) text |                                     |               |
   |intact          |                                     |               |
   +----------------+-------------------------------------+---------------+
   |markup language |just an appendix                     |~4 different   |
   +----------------+-------------------------------------+---------------+
   |polyglot format |no                                   |yes            |
   +----------------+-------------------------------------+---------------+
   |easy to copy/   |yes                                  |up to          |
   |paste           |                                     |application    |
   |content+metadata|                                     |               |
   +----------------+-------------------------------------+---------------+
   |easy to write/  |yes                                  |depends        |
   |repair for      |                                     |               |
   |layman          |                                     |               |
   +----------------+-------------------------------------+---------------+
   |easy to         |yes (fits on A4 paper)               |depends        |
   |(de)serialize   |                                     |               |
   +----------------+-------------------------------------+---------------+
   |infrastructure  |selfcontained (plain text)           |(semi)networked|
   +----------------+-------------------------------------+---------------+
   |freeform        |yes, terse                           |yes, verbose   |
   |tagging/        |                                     |               |
   |annotation      |                                     |               |
   +----------------+-------------------------------------+---------------+
   |can be appended |yes                                  |up to          |
   |to text-content |                                     |application    |
   +----------------+-------------------------------------+---------------+
   |copy-paste text |yes                                  |up to          |
   |preserves       |                                     |application    |
   |metadata        |                                     |               |
   +----------------+-------------------------------------+---------------+



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   |emoji           |yes                                  |depends on     |
   |                |                                     |encoding       |
   +----------------+-------------------------------------+---------------+
   |predicates      |free                                 |semi pre-      |
   |                |                                     |determined     |
   +----------------+-------------------------------------+---------------+
   |implementation/ |no                                   |depends        |
   |network overhead|                                     |               |
   +----------------+-------------------------------------+---------------+
   |used in         |yes (visual-meta)                    |no             |
   |(physical)      |                                     |               |
   |books/PDF       |                                     |               |
   +----------------+-------------------------------------+---------------+
   |terse non-verb  |yes                                  |no             |
   |predicates      |                                     |               |
   +----------------+-------------------------------------+---------------+
   |nested          |no (but: BibTex rulers)              |yes            |
   |structures      |                                     |               |
   +----------------+-------------------------------------+---------------+

                                  Table 6

9.4.  XR Text example parser

   1.  The XR Fragments spec does not aim to harden the BiBTeX format
   2.  However, respect multi-line BibTex values because of the core
       principle (#core-principle)
   3.  Expand bibs and rulers (like ${visual-meta-start}) according to
       the tagbibs spec (https://github.com/coderofsalvation/tagbibs)
   4.  BibTeX snippets should always start in the beginning of a line
       (regex: ^@), hence mimetype text/plain;charset=utf-8;bib=^@

   Here's an XR Text (de)multiplexer in javascript, which ticks all the
   above boxes:

xrtext = {

  decode: (str) => {
         // bibtex:     ↓@   ↓<tag|tag{phrase,|{ruler}>  ↓property  ↓end
         let pat    = [ /@/, /^\S+[,{}]/,                /},/,      /}/ ]
         let tags   = [], text='', i=0, prop=''
         var bibs   = { regex: /(@[a-zA-Z0-9_+]+@[a-zA-Z0-9_@]+)/g, tags: {}}
         let lines  = str.replace(/\r?\n/g,'\n').split(/\n/)
         for( let i = 0; !lines[i].match( /^@/ ); i++ ) text += lines[i]+'\n'

         bibtex = lines.join('\n').substr( text.length )
         bibtex.replace( bibs.regex , (m,k,v) => {
             tok   = m.substr(1).split("@")



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             match = tok.shift()
             tok.map( (t) => bibs.tags[match] = `@${t}{${match},\n}\n` )
         })
         bibtex = Object.values(bibs.tags).join('\n') + bibtex.replace( bibs.regex, '')
         bibtex.split( pat[0] ).map( (t) => {
             try{
                let v = {}
                if( !(t = t.trim())         ) return
                if( tag = t.match( pat[1] ) ) tag = tag[0]
                if( tag.match( /^{.*}$/ )   ) return tags.push({ruler:tag})
                t = t.substr( tag.length )
                t.split( pat[2] )
                .map( kv => {
                  if( !(kv = kv.trim()) || kv == "}" ) return
                  v[ kv.match(/\s?(\S+)\s?=/)[1] ] = kv.substr( kv.indexOf("{")+1 )
                })
                tags.push( { k:tag, v } )
             }catch(e){ console.error(e) }
        })
        return {text, tags}
  },

  encode: (text,tags) => {
    let str = text+"\n"
    for( let i in tags ){
      let item = tags[i]
      if( item.ruler ){
          str += `@${item.ruler}\n`
          continue;
      }
      str += `@${item.k}\n`
      for( let j in item.v ) str += `  ${j} = {${item.v[j]}}\n`
      str += `}\n`
    }
    return str
  }
}

   The above functions (de)multiplexe text/metadata, expands bibs,
   (de)serialize bibtex (and all fits more or less on one A4 paper)

   |  above can be used as a startingpoint for LLVM's to translate/
   |  steelman to a more formal form/language.








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str = `
hello world

@hello@greeting
@{some-section}
@flap{
  asdf = {23423}
}`

var {tags,text} = xrtext.decode(str)          // demultiplex text & bibtex
tags.find( (t) => t.k == 'flap{' ).v.asdf = 1 // edit tag
tags.push({ k:'bar{', v:{abc:123} })          // add tag
console.log( xrtext.encode(text,tags) )       // multiplex text & bibtex back together

   This outputs:

   hello world


   @greeting{hello,
   }
   @{some-section}
   @flap{
     asdf = {1}
   }
   @bar{
     abc = {123}
   }

10.  HYPER copy/paste

   The previous example, offers something exciting compared to simple
   copy/paste of 3D objects or text.  XR Text according to the XR
   Fragment spec, allows HYPER-copy/paste: time, space and text
   interlinked.  Therefore, the enduser in an XR Fragment-compatible
   browser can copy/paste/share data in these ways:

   1.  time/space: 3D object (current animation-loop)
   2.  text: TeXt object (including BibTeX/visual-meta if any)
   3.  interlinked: Collected objects by visual-meta tag

11.  Security Considerations

   Since XR Text contains metadata too, the user should be able to set
   up tagging-rules, so the copy-paste feature can :

   *  filter out sensitive data when copy/pasting (XR text with
      class:secret e.g.)



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12.  IANA Considerations

   This document has no IANA actions.

13.  Acknowledgments

   *  NLNET (https://nlnet.nl)
   *  Future of Text (https://futureoftext.org)
   *  visual-meta.info (https://visual-meta.info)

14.  Appendix: Definitions

     +===============+==============================================+
     | definition    | explanation                                  |
     +===============+==============================================+
     | human         | a sentient being who thinks fuzzy, absorbs,  |
     |               | and shares thought (by plain text, not       |
     |               | markuplanguage)                              |
     +---------------+----------------------------------------------+
     | scene         | a (local/remote) 3D scene or 3D file         |
     |               | (index.gltf e.g.)                            |
     +---------------+----------------------------------------------+
     | 3D object     | an object inside a scene characterized by    |
     |               | vertex-, face- and customproperty data.      |
     +---------------+----------------------------------------------+
     | metadata      | custom properties of text, 3D Scene or       |
     |               | Object(nodes), relevant to machines and a    |
     |               | human minority (academics/developers)        |
     +---------------+----------------------------------------------+
     | XR fragment   | URI Fragment with spatial hints like         |
     |               | #pos=0,0,0&t=1,100 e.g.                      |
     +---------------+----------------------------------------------+
     | src           | (HTML-piggybacked) metadata of a 3D object   |
     |               | which instances content                      |
     +---------------+----------------------------------------------+
     | href          | (HTML-piggybacked) metadata of a 3D object   |
     |               | which links to content                       |
     +---------------+----------------------------------------------+
     | query         | an URI Fragment-operator which queries       |
     |               | object(s) from a scene like #q=cube          |
     +---------------+----------------------------------------------+
     | visual-meta   | visual-meta (https://visual.meta.info) data  |
     |               | appended to text/books/papers which is       |
     |               | indirectly visible/editable in XR.           |
     +---------------+----------------------------------------------+
     | requestless   | metadata which never spawns new requests     |
     | metadata      | (unlike RDF/HTML, which can cause framerate- |
     |               | dropping, hence not used a lot in games)     |



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     +---------------+----------------------------------------------+
     | FPS           | frames per second in spatial experiences     |
     |               | (games,VR,AR e.g.), should be as high as     |
     |               | possible                                     |
     +---------------+----------------------------------------------+
     | introspective | inward sensemaking ("I feel this belongs to  |
     |               | that")                                       |
     +---------------+----------------------------------------------+
     | extrospective | outward sensemaking ("I'm fairly sure John   |
     |               | is a person who lives in oklahoma")          |
     +---------------+----------------------------------------------+
     | &#9723;       | ascii representation of an 3D object/mesh    |
     +---------------+----------------------------------------------+
     | (un)obtrusive | obtrusive: wrapping human text/thought in    |
     |               | XML/HTML/JSON obfuscates human text into a   |
     |               | salad of machine-symbols and words           |
     +---------------+----------------------------------------------+
     | BibTeX        | simple tagging/citing/referencing standard   |
     |               | for plaintext                                |
     +---------------+----------------------------------------------+
     | BibTag        | a BibTeX tag                                 |
     +---------------+----------------------------------------------+

                                 Table 7



























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