MU part 3: More MUD

Apologies to people reading this via LiveJournal's syndicated feed; a combination of my software converting every header in to an RSS item and LiveJournal duplicating each item every time I edited the title has created a flurry of links to essays that I expect no-one but me has any interest in anyway.

Just to rub it in, here is some more of my imaginary generalized mark-up language MU and its metadata format MUD..

No-range tags

The property no-range tags is a list of etypes, as a YAML list:

no-range tags:
  - img
  - embed
  - applet
  - br
  - hr
  - base
  - link

This is a kludge to allow for HTML's empty elements: a list of etypes for which the no-range-tag syntax is permitted. For example, with the above definition, <hr> is treated the same as <hr/>.

It is in the MUD file -- rather than being in a separate schema or pattern file -- because it is needed to parse the MU. This sadly means documents using this feature are not stand-alone.

Character entities

This section is used to define additional character entities.

    nbsp: 00A0
    iexcl: 00A1
    cent: 00A2

Characters are defined here using Unicode code points in hexadecimal, so that in this example, &iexcl; is equivalent to &#x00A1;. Note that (unlike SGML and XML) we do not allow entities to expand to more than one character.

Style sheets

Collections of documents that describe how to display the text. I am supposing in these examples that in the parallel universe where MU is defined, CSS has been extended to work with documents containing overlapping mark-up in the style of LMNL and MU.

        title: Standard appearance
    media: screen
        style sheets:
          - foo.css
      - bar.css
        title: Compact layout
    media: screen
        style sheets:
      - foo.css
      - bar-compact.css

The view named default is used initially; all the other view names are arbitrary, and are there for the sake of style-sheet switchers. The features tag says which style-sheet processors will be required to make sense of this view; if that feature is missing, that view is skipped. This gives a way to extend the style-sheet system, without using special mdia-types for the CSS files.

It might be reasonable to make the CSS feature mandatory, so that in the common case the features tag is not needed.

This is just a sketch -- sorting out the details is left as an excerise for the reader.


MUD files can also contain arbitrary extra data for plug-ins to play with. This is a special section called extensions:

        default-voice: tiny child
    default-speed: 110%
      - this.rng
      - that.rnc
        mode: pedantic

The keys are arbitrary. Generally there should be a corresponding features entry that activates the plug-in that then searches the extensions section for its configuration, if any.

MUD versus MUM versus META

Some of the fields I outlined for MUD files -- such as type and charset -- I now think deserve a file of their own, which I have dubbed META. The MUD file therefore is a document-format definition, shared by many documents, compared with the META file, which gives information specific to a single document.

The description of META files now moved out to its own page.

MUM is a bundling format I will describe some time in the future.


Updated 2004-08-05 to add characters, extensions and views sections.