Provided by: tcllib_1.19-dfsg-2_all 
NAME
doctoc_plugin_apiref - doctoc plugin API reference
SYNOPSIS
dt_fmap symfname
dt_format
dt_read file
dt_source file
ex_cappend text
ex_cget varname
ex_cis cname
ex_cname
ex_cpop cname
ex_cpush cname
ex_cset varname value
ex_lb ?newbracket?
ex_rb ?newbracket?
toc_initialize
toc_listvariables
toc_numpasses
toc_postprocess text
toc_setup n
toc_shutdown
toc_varset varname text
fmt_plain_text text
________________________________________________________________________________________________________________
DESCRIPTION
This document is intended for plugin writers, i.e. developers wishing to write a toc formatting engine
for some output format X.
It specifies the interaction between the doctools::toc package and its plugins, i.e. the interface any
toc formatting engine has to comply with.
This document deals with version 1 of the interface.
A reader who is on the other hand more interested in the markup language itself should start with the
doctoc language introduction and proceed from there to the formal specifications, i.e. the doctoc
language syntax and the doctoc language command reference.
OVERVIEW
The API for a toc formatting engine consists of two major sections.
On the one side we have a set of commands through which the plugin is able to query the frontend. These
commands are provided by the frontend and linked into the plugin interpreter. Please see section FRONTEND
COMMANDS for their detailed specification.
And on the other side the plugin has to provide its own set of commands which will then be called by the
frontend in a specific sequence while processing input. They, again, fall into two categories, management
and formatting. Please see section PLUGIN COMMANDS and its subsections for their detailed specification.
FRONTEND COMMANDS
This section specifies the set of commands through which a plugin, also known as a toc formatting engine,
is able to query the frontend. These commands are provided by the frontend and linked into the plugin
interpreter.
I.e. a toc formatting engine can assume that all of the following commands are present when any of its
own commands (as specified in section PLUGIN COMMANDS) are executed.
Beyond that it can also assume that it has full access to its own safe interpreter and thus is not able
to damage the other parts of the processor, nor can it damage the filesystem. It is however able to
either kill or hang the whole process, by exiting, or running an infinite loop.
Coming back to the imported commands, all the commands with prefix dt_ provide limited access to specific
parts of the frontend, whereas the commands with prefix ex_ provide access to the state of the
textutil::expander object which does the main parsing of the input within the frontend. These commands
should not be except under very special circumstances.
dt_fmap symfname
Query command. It returns the actual pathname to use in the output in place of the symbolic
filename symfname. It will return the unchanged input if no mapping was established for symfname.
The required mappings are established with the method map of a frontend, as explained in section
OBJECT METHODS of the documentation for the package doctools::toc.
dt_format
Query command. It returns the name of the format associated with the toc formatting engine.
dt_read file
Controlled filesystem access. Returns contents of file for whatever use desired by the plugin.
Only files which are either in the same directory as the file containing the engine, or below it,
can be loaded. Trying to load a file outside of this directory causes an error.
dt_source file
Controlled filesystem access. This command allows the toc formatting engine to load additional Tcl
code it may need. Only files which are either in the same directory as the file containing the
engine, or below it, can be loaded. Trying to load a file outside of this directory causes an
error.
ex_cappend text
Appends a string to the output in the current context. This command should rarely be used by
macros or application code.
ex_cget varname
Retrieves the value of variable varname, defined in the current context.
ex_cis cname
Determines whether or not the name of the current context is cname.
ex_cname
Returns the name of the current context.
ex_cpop cname
Pops a context from the context stack, returning all accumulated output in that context. The
context must be named cname, or an error results.
ex_cpush cname
Pushes a context named cname onto the context stack. The context must be popped by cpop before
expansion ends or an error results.
ex_cset varname value
Sets variable varname to value in the current context.
ex_lb ?newbracket?
Returns the current value of the left macro expansion bracket; this is for use as or within a
macro, when the bracket needs to be included in the output text. If newbracket is specified, it
becomes the new bracket, and is returned.
ex_rb ?newbracket?
Returns the current value of the right macro expansion bracket; this is for use as or within a
macro, when the bracket needs to be included in the output text. If newbracket is specified, it
becomes the new bracket, and is returned.
PLUGIN COMMANDS
The plugin has to provide its own set of commands which will then be called by the frontend in a specific
sequence while processing input. They fall into two categories, management and formatting. Their expected
names, signatures, and responsibilities are specified in the following two subsections.
MANAGEMENT COMMANDS
The management commands a plugin has to provide are used by the frontend to
[1] initialize and shutdown the plugin
[2] determine the number of passes it has to make over the input
[3] initialize and shutdown each pass
[4] query and initialize engine parameters
After the plugin has been loaded and the frontend commands are established the commands will be called in
the following sequence:
toc_numpasses -> n
toc_listvariables -> vars
toc_varset var1 value1
toc_varset var2 value2
...
toc_varset varK valueK
toc_initialize
toc_setup 1
...
toc_setup 2
...
...
toc_setup n
...
toc_postprocess
toc_shutdown
...
I.e. first the number of passes and the set of available engine parameters is established, followed by
calls setting the parameters. That second part is optional.
After that the plugin is initialized, the specified number of passes executed, the final result run
through a global post processing step and at last the plugin is shutdown again. This can be followed by
more conversions, restarting the sequence at toc_varset.
In each of the passes, i.e. after the calls of toc_setup the frontend will process the input and call the
formatting commands as markup is encountered. This means that the sequence of formatting commands is
determined by the grammar of the doctoc markup language, as specified in the doctoc language syntax
specification.
A different way of looking at the sequence is:
• First some basic parameters are determined.
• Then everything starting at the first toc_varset to toc_shutdown forms a run, the formatting of a
single input. Each run can be followed by more.
• Embedded within each run we have one or more passes, each starting with toc_setup and going until
either the next toc_setup or toc_postprocess is reached.
If more than one pass is required to perform the formatting only the output of the last pass is
relevant. The output of all the previous, preparatory passes is ignored.
The commands, their names, signatures, and responsibilities are, in detail:
toc_initialize
Initialization/Shutdown. This command is called at the beginning of every conversion run, as the
first command of that run. Note that a run is not a pass, but may consist of multiple passes. It
has to initialize the general state of the plugin, beyond the initialization done during the load.
No return value is expected, and any returned value is ignored.
toc_listvariables
Initialization/Shutdown and Engine parameters. Second command is called after the plugin code has
been loaded, i.e. immediately after toc_numpasses. It has to return a list containing the names
of the parameters the frontend can set to configure the engine. This list can be empty.
toc_numpasses
Initialization/Shutdown and Pass management. First command called after the plugin code has been
loaded. No other command of the engine will be called before it. It has to return the number of
passes this engine requires to fully process the input document. This value has to be an integer
number greater or equal to one.
toc_postprocess text
Initialization/Shutdown. This command is called immediately after the last pass in a run. Its
argument is the result of the conversion generated by that pass. It is provided to allow the
engine to perform any global modifications of the generated document. If no post-processing is
required for a specific format the command has to just return the argument.
Expected to return a value, the final result of formatting the input.
toc_setup n
Initialization/Shutdown and Pass management. This command is called at the beginning of each pass
over the input in a run. Its argument is the number of the pass which has begun. Passes are
counted from 1 upward. The command has to set up the internal state of the plugin for this
particular pass. No return value is expected, and any returned value is ignored.
toc_shutdown
Initialization/Shutdown. This command is called at the end of every conversion run. It is the
last command called in a run. It has to clean up of all the run-specific state in the plugin.
After the call the engine has to be in a state which allows the initiation of another run without
fear that information from the last run is leaked into this new run. No return value is expected,
and any returned value is ignored.
toc_varset varname text
Engine parameters. This command is called by the frontend to set an engine parameter to a
particular value. The parameter to change is specified by varname, the value to set in text.
The command has to throw an error if an unknown varname is used. Only the names returned by
toc_listvariables have to be considered as known.
The values of all engine parameters have to persist between passes and runs.
FORMATTING COMMANDS
The formatting commands have to implement the formatting for the output format, for all the markup
commands of the doctoc markup language, except lb, rb, vset, include, and comment. These exceptions are
processed by the frontend and are never seen by the plugin. In return a command for the formatting of
plain text has to be provided, something which has no markup in the input at all.
This means, that each of the five markup commands specified in the doctoc language command reference and
outside of the set of exceptions listed above has an equivalent formatting command which takes the same
arguments as the markup command and whose name is the name of markup command with the prefix fmt_ added
to it.
All commands are expected to format their input in some way per the semantics specified in the command
reference and to return whatever part of this that they deem necessary as their result, which will be
added to the output.
To avoid essentially duplicating the command reference we do not list any of the command here and simply
refer the reader to the doctoc language command reference for their signature and description. The sole
exception is the plain text formatter, which has no equivalent markup command.
The calling sequence of formatting commands is not as rigid as for the management commands, but
determined by the grammar of the doctoc markup language, as specified in the doctoc language syntax
specification.
fmt_plain_text text
No associated markup command.
Called by the frontend for any plain text encountered in the input. It has to perform any and all
special processing required for plain text.
The formatted text is expected as the result of the command, and added to the output. If no
special processing is required it has to simply return its argument without change.
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please
report such in the category doctools of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist].
Please also report any ideas for enhancements you may have for either package and/or documentation.
When proposing code changes, please provide unified diffs, i.e the output of diff -u.
Note further that attachments are strongly preferred over inlined patches. Attachments can be made by
going to the Edit form of the ticket immediately after its creation, and then using the left-most button
in the secondary navigation bar.
SEE ALSO
doctoc_intro, doctoc_lang_cmdref, doctoc_lang_faq, doctoc_lang_intro, doctoc_lang_syntax, doctools::toc
KEYWORDS
formatting engine, markup, plugin, semantic markup, table of contents, toc, toc formatter
CATEGORY
Documentation tools
COPYRIGHT
Copyright (c) 2007 Andreas Kupries <andreas_kupries@users.sourceforge.net>