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%%% Title = "XR Fragments" area = "Internet" workgroup = "Internet Engineering Task Force"

[seriesInfo] name = "XR-Fragments" value = "draft-XRFRAGMENTS-leonvankammen-00" stream = "IETF" status = "informational"

date = 2023-04-12T00:00:00Z

author initials="L.R." surname="van Kammen" fullname="L.R. van Kammen"

%%%

.# 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 annotating 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 and BibTags notation.

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

{mainmatter}

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 + src/href spatial metadata
  2. Interlinking text/& 3D by collapsing space into a Word Graph (XRWG) (and augmenting text with bibs / BibTags appendices (see visual-meta e.g.)

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

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).

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.

Conventions and Definitions

See appendix below in case certain terms are not clear.

XR Fragment URI Grammar

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

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

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 #cube object(s) of interest (fragment-to-object-or-classname)

xyz coordinates are similar to ones found in SVG Media Fragments

List of metadata for 3D nodes

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

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.

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)
  |                                                        |
  +--------------------------------------------------------+

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.

Embedding 3D content

Here's an ascii representation of a 3D scene-graph with 3D objects ◻ which embeds remote & local 3D objects ◻ with/out using queries:

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

Instead of cherrypicking objects with #bass&tuna thru src, queries can be used to import the whole scene (and filter out certain objects). See next chapter below.

XR Fragment queries

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

example outcome
#q=-sky show everything except object named sky
#q=-.language .english hide everything with class language, but show all class english objects
#q=price:>2 price:<5 of all objects with property price, show only objects with value between 2 and 5

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

  1. queries are a way to traverse a scene, and filter objects based on their class- or property-values.
  2. words starting with . like .german match class-metadata of 3D objects like "class":"german"
  3. 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.

including/excluding

operator info
- 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) (*)

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

» example implementation » example 3D asset » discussion

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

Embedding local/remote content (instancing)

src is the 3D version of the iframe.
It instances content (in objects) in the current scene/asset.

fragment type example value
src string (uri or [[predefined view predefined_view]] or [[query
  1. local/remote content is instanced by the src (query) value (and attaches it to the placeholder mesh containing the src property)
  2. local src values (URL starting with #, like #cube&foo) means only the mentioned objectnames will be copied to the instanced scene (from the current scene) while preserving their names (to support recursive selectors). (example code)
  3. local src values indicating a query (#q=), means that all included objects (from the current scene) will be copied to the instanced scene (before applying the query) while preserving their names (to support recursive selectors). (example code)
  4. the instanced scene (from a src value) should be scaled accordingly to its placeholder object or scaled relatively based on the scale-property (of a geometry-less placeholder, an 'empty'-object in blender e.g.). For more info see Chapter Scaling.
  5. external src (file) values should be served with appropriate mimetype (so the XR Fragment-compatible browser will now how to render it). The bare minimum supported mimetypes are:
  6. when only one object was cherrypicked (#cube e.g.), set its position to 0,0,0
  • model/gltf+json
  • image/png
  • image/jpg
  • text/plain;charset=utf-8;bib=^@

Scaling instanced content

Text in XR (tagging,linking to spatial objects)

How does XR Fragments interlink text with objects?

The XR Fragments does this by collapsing space into a Word Graph (the XRWG), augmented by Bib(s)Tex.

Instead of just throwing together all kinds media types into one experience (games), what about the intrinsic connections between them?
Why is HTML adopted less in games outside the browser? Through the lens of game-making, ideally metadata must come with that text, but not obfuscate the text, or spawning another request to fetch it.
XR Fragments does this by detecting Bib(s)Tex, without introducing a new language or fileformat

Why Bib(s)Tex? Because its seems to be the lowest common denominator for an human-curated XRWG (extendable by speech/scanner/writing/typing e.g, see further motivation here)

Hence:

  1. XR Fragments promotes (de)serializing a scene to the XRWG
  2. XR Fragments primes the XRWG, by collecting words from the class and name-property of 3D objects.
  3. XR Fragments primes the XRWG, by collecting words from optional metadata at the end of content of text (see default mimetype & Data URI)
  4. Bib's and BibTex are first class citizens for priming the XRWG with words (from XR text)
  5. Like Bibs, XR Fragments generalizes the BibTex author/title-semantics (author{title}) into this points to that (this{that})
  6. The XRWG should be recalculated when textvalues (in src) change
  7. HTML/RDF/JSON is still great, but is beyond the XRWG-scope (they fit better in the application-layer)
  8. Applications don't have to be able to access the XRWG programmatically, as they can easily generate one themselves by traversing the scene-nodes.
  9. The XR Fragment focuses on fast and easy-to-generate end-user controllable word graphs (instead of complex implementations that try to defeat word ambiguity)

Example:

  http://y.io/z.fbx                                                           | Derived XRWG (printed as BibTex)
  ----------------------------------------------------------------------------+--------------------------------------
                                                                              | @house{castle,
  +-[src: data:.....]----------------------+   +-[3D mesh]-+                  |   url = {https://y.io/z.fbx#castle}
  | Chapter one                            |   |    / \    |                  | }
  |                                        |   |   /   \   |                  | @baroque{castle,
  | John built houses in baroque style.    |   |  /     \  |                  |   url = {https://y.io/z.fbx#castle}
  |                                        |   |  |_____|  |                  | }
  | #john@baroque                          |   +-----│-----+                  | @baroque{john}
  |                                        |         │                        |
  |                                        |         ├─ name: castle          | 
  |                                        |         └─ class: house baroque  | 
  +----------------------------------------+                                  |
                                               [3D mesh ]                     |
                                               |    O   ├─ name: john         |                           
                                               |   /|\  |                     |
                                               |   / \  |                     |
                                               +--------+                     |

the #john@baroque-bib associates both text John and objectname john, with class baroque


Another example:

http://y.io/z.fbx | Derived XRWG (printed as BibTex) ----------------------------------------------------------------------------+-------------------------------------- | +-[src: data:.....]----------------------+ +-[3D mesh]-+ | @house{castle, | Chapter one | | / \ | | url = {https://y.io/z.fbx#castle} | | | / \ | | } | John built houses in baroque style. | | / \ | | @baroque{castle, | | | |_____| | | url = {https://y.io/z.fbx#castle} | #john@baroque | +-----│-----+ | } | @baroque{john} | │ | @baroque{john} | | ├─ name: castle | | | └─ class: house baroque | +----------------------------------------+ | @house{baroque} [3D mesh ] | @todo{baroque} +-[remotestorage.io / localstorage]------+ | O + name: john | | #baroque@todo@house | | /|\ | | | ... | | / \ | | +----------------------------------------+ +--------+ |


> both `#john@baroque`-bib and BibTex `@baroque{john}` result in the same XRWG, however on top of that 2 classes (`house` and `todo`) are now associated with text/objectname/class 'baroque'.

As seen above, the XRWG can expand [bibs](https://github.com/coderofsalvation/hashtagbibs) (and the whole scene) to BibTeX.<br>
This allows hasslefree authoring and copy-paste of associations **for and by humans**, but also makes these URLs possible:

| URL example                           | Result                                                                    |
|---------------------------------------|---------------------------------------------------------------------------|
| `https://my.com/foo.gltf#.baroque`    | highlights mesh `john`, 3D mesh `castle`, text `John built(..)`           |
| `https://my.com/foo.gltf#john`        | highlights mesh `john`, and the text `John built (..)`                    |
| `https://my.com/foo.gltf#house`       | highlights mesh `castle`, and other objects with class `house` or `todo`  |

> [hashtagbibs](https://github.com/coderofsalvation/hashtagbibs) potentially allow the enduser to annotate text/objects by **speaking/typing/scanning associations**, which the XR Browser saves to remotestorage (or localStorage per toplevel URL). As well as, referencing BibTags per URI later on: `https://y.io/z.fbx#@baroque@todo` e.g.

The XRWG allows XR Browsers to show/hide relationships in realtime at various levels:

* wordmatch **inside** `src` text 
* wordmatch **inside** `href` text
* wordmatch object-names 
* wordmatch object-classnames 

Spatial wires can be rendered, words/objects can be highlighted/scaled etc.<br>
Some pointers for good UX (but not necessary to be XR Fragment compatible):

9. 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)
10. 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.
12. respect multi-line BiBTeX metadata in text because of [the core principle](#core-principle)
13. Default font (unless specified otherwise) is a modern monospace font, for maximized tabular expressiveness (see [the core principle](#core-principle)).
14. anti-pattern: hardcoupling an XR Browser with a mandatory **markup/scripting-language** which departs from onubtrusive plain text (HTML/VRML/Javascript) (see [the core principle](#core-principle))
15. anti-pattern: limiting human introspection, by abandoning plain text as first class citizen.

> The simplicity of appending metadata (and leveling the metadata-playfield between humans and machines) is also demonstrated by [visual-meta](https://visual-meta.info) in greater detail.

Fictional chat:

Hey what about this: https://my.com/station.gltf#pos=0,0,1&rot=90,2,0&t=500,1000 I'm checking it right now I don't see everything..where's our text from yesterday? Ah wait, that's tagged with class 'draft' (and hidden)..hold on, try this: https://my.com/station.gltf#.draft&pos=0,0,1&rot=90,2,0&t=500,1000 how about we link the draft to the upcoming YELLO-event? ok I'm adding #draft@YELLO Yesterday I also came up with other usefull assocations between other texts in the scene: #event#YELLO #2025@YELLO thanks, added. Btw. I stumbled upon this spatial book which references station.gltf in some chapters: https://thecommunity.org/forum/foo/mytrainstory.txt interesting, I'm importing mytrainstory.txt into station.gltf ah yes, chapter three points to trainterminal_2A, cool


## 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 hashtagbib(tex)-friendly one:

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

This indicates that:

* utf-8 is supported by default
* lines beginning with `@` will not be rendered verbatim by default ([read more](https://github.com/coderofsalvation/hashtagbibs#hashtagbib-mimetypes))
* the XRWG should expand bibs to BibTex occurring in text (`#contactjohn@todo@important` e.g.) 

By doing so, the XR Browser (applications-layer) can interpret microformats ([visual-meta](https://visual-meta.info) 
to connect text further with its environment ( setup links between textual/spatial objects automatically e.g.).

> for more info on this mimetype see [bibs](https://github.com/coderofsalvation/hashtagbibs)

Advantages: 

* auto-expanding of [hashtagbibs](https://github.com/coderofsalvation/hashtagbibs) associations
* out-of-the-box (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 

> 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).<br>

## URL and Data URI

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


The enduser will only see `welcome human` and `Hello friends` rendered verbatim (see mimetype).
The beauty is that text in Data URI automatically promotes rich copy-paste (retaining metadata).
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/hashtagbibs): to tag spatial object `note_canvas` with 'todo', the enduser can type or speak `#note_canvas@todo`

## XR Text example parser 

To prime the XRWG with text from plain text `src`-values, here's an example XR Text (de)multiplexer in javascript (which supports inline bibs & bibtex):

xrtext = {

expandBibs: (text) => { let bibs = { regex: /(#[a-zA-Z0-9_+@-]+(#)?)/g, tags: {}} text.replace( bibs.regex , (m,k,v) => { tok = m.substr(1).split("@") match = tok.shift() if( tok.length ) tok.map( (t) => bibs.tags[t] = @${t}{${match},\n} ) else if( match.substr(-1) == '#' ) bibs.tags[match] = @{${match.replace(/#/,'')}} else bibs.tags[match] = @${match}{${match},\n} }) return text.replace( bibs.regex, '') + Object.values(bibs.tags).join('\n') },

decode: (str) => { // bibtex: ↓@ ↓<tag|tag{phrase,|{ruler}> ↓property ↓end let pat = [ /@/, /^\S+[,{}]/, /},/, /}/ ] let tags = [], text='', i=0, prop='' let lines = xrtext.expandBibs(str).replace(/\r?\n/g,'\n').split(/\n/) for( let i = 0; i < lines.length && !String(lines[i]).match( /^@/ ); i++ ) text += lines[i]+'\n'

bibtex = lines.join('\n').substr( text.length )
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( /^{.*}$/ )   ) return tags.push({ruler:tag})
       if( tag.match( /}$/ )       ) return tags.push({k: tag.replace(/}$/,''), v: {}})
       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 vice versa

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

str = ` hello world here are some hashtagbibs followed by bibtex:

#world #hello@greeting #another-section#

@{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 expands to the following (hidden by default) BibTex appendix:

hello world here are some hashtagbibs followed by bibtex:

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


> when an XR browser updates the human text, a quick scan for nonmatching tags (`@book{nonmatchingbook` e.g.) should be performed and prompt the enduser for deleting them.

# 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.)

# IANA Considerations

This document has no IANA actions.

# Acknowledgments

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

# 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  | metadata which never spawns new requests (unlike RDF/HTML, which can cause framerate-dropping, hence not used a lot in games)        |
|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")                                                       |
|`◻`                   | 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                                                                                                                         |
|(hashtag)bibs         | an easy to speak/type/scan tagging SDL ([see here](https://github.com/coderofsalvation/hashtagbibs) which expands to BibTex/JSON/XML |