docidx_lang_intro(n) 1.0 tcllib "Documentation tools"

Fundamentals

While the docidx markup language is quite similar to the doctools markup language, in the broadest terms possible, there is one key difference. An index consists essentially only of markup commands, with no plain text interspersed between them, except for whitespace.

Each markup command is a Tcl command surrounded by a matching pair of [ and ]. Inside of these delimiters the usual rules for a Tcl command apply with regard to word quotation, nested commands, continuation lines, etc. I.e.

    ... [key {markup language}] ...

  ... [manpage thefile \\
          {file description}] ...

Basic structure

The most simple document which can be written in docidx is

    [index_begin GROUPTITLE TITLE]
    [index_end]

Not very useful, but valid. This also shows us that all docidx documents consist of only one part where we will list all keys and their references.

A more useful index will contain at least keywords, or short 'keys', i.e. the phrases which were indexed. So:

[index_begin GROUPTITLE TITLE]
[key markup]
[key {semantic markup}]]
[key {docidx markup}]
[key {docidx language}]
[key {docidx commands}]
[index_end]

In the above example the command key is used to declare the keyword phrases we wish to be part of the index.

However a truly useful index does not only list the keyword phrases, but will also contain references to documents associated with the keywords. Here is a made-up index for all the manpages in the module base64:

[index_begin tcllib/base64 {De- & Encoding}]
[key base64]
[manpage base64]
[key encoding]
[manpage base64]
[manpage uuencode]
[manpage yencode]
[key uuencode]
[manpage uuencode]
[key yEnc]
[manpage yencode]
[key ydecode]
[manpage yencode]
[key yencode]
[manpage yencode]
[index_end]

In the above example the command manpage is used to insert references to documents, using symbolic file names, with each command belonging to the last key command coming before it.

The other command to insert references is url. In contrast to manpage it uses explicit (possibly format-specific) urls to describe the location of the referenced document. As such this command is intended for the creation of references to external documents which could not be handled in any other way.

Advanced structure

In all previous examples we fudged a bit regarding the markup actually allowed to be used before the index_begin command opening the document.

Instead of only whitespace the two templating commands include and vset are also allowed, to enable the writer to either set and/or import configuration settings relevant to the table of contents. I.e. it is possible to write

[include FILE]
[vset VAR VALUE]
[index_begin GROUPTITLE TITLE]
...
[index_end]

Even more important, these two commands are allowed anywhere where a markup command is allowed, without regard for any other structure.

[index_begin GROUPTITLE TITLE]
[include FILE]
[vset VAR VALUE]
...
[index_end]

The only restriction include has to obey is that the contents of the included file must be valid at the place of the inclusion. I.e. a file included before index_begin may contain only the templating commands vset and include, a file included after a key may contain only manape or url references, and other keys, etc.

Escapes

Beyond the 6 commands shown so far we have two more available. However their function is not the marking up of index structure, but the insertion of characters, namely [ and ]. These commands, lb and rb respectively, are required because our use of [ and ] to bracket markup commands makes it impossible to directly use [ and ] within the text.

Our example of their use are the sources of the last sentence in the previous paragraph, with some highlighting added.

  ...
  These commands, [cmd lb] and [cmd lb] respectively, are required
  because our use of [lb] and [rb] to bracket markup commands makes it
  impossible to directly use [lb] and [rb] within the text.
  ...