Provided by: tcllib_1.17-dfsg-1_all 
NAME
docidx_plugin_apiref - docidx 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?
idx_initialize
idx_listvariables
idx_numpasses
idx_postprocess text
idx_setup n
idx_shutdown
idx_varset varname text
fmt_plain_text text
_________________________________________________________________________________________________
DESCRIPTION
This document is intended for plugin writers, i.e. developers wishing to write an index
formatting engine for some output format X.
It specifies the interaction between the doctools::idx package and its plugins, i.e. the
interface any index 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 docidx language introduction and proceed from there to the formal
specifications, i.e. the docidx language syntax and the docidx language command reference.
OVERVIEW
The API for an index 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 an index
formatting engine, is able to query the frontend. These commands are provided by the
frontend and linked into the plugin interpreter.
I.e. an index 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::idx.
dt_format
Query command. It returns the name of the format associated with the index
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 index 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:
idx_numpasses -> n
idx_listvariables -> vars
idx_varset var1 value1
idx_varset var2 value2
...
idx_varset varK valueK
idx_initialize
idx_setup 1
...
idx_setup 2
...
...
idx_setup n
...
idx_postprocess
idx_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 idx_varset.
In each of the passes, i.e. after the calls of idx_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 docidx markup
language, as specified in the docidx language syntax specification.
A different way of looking at the sequence is:
• First some basic parameters are determined.
• Then everything starting at the first idx_varset to idx_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 idx_setup
and going until either the next idx_setup or idx_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:
idx_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.
idx_listvariables
Initialization/Shutdown and Engine parameters. Second command is called after the
plugin code has been loaded, i.e. immediately after idx_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.
idx_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.
idx_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.
idx_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.
idx_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.
idx_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 idx_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 docidx 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 docidx 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 docidx 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 docidx markup language, as specified in the
docidx 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.
SEE ALSO
docidx_intro, docidx_lang_cmdref, docidx_lang_faq, docidx_lang_intro, docidx_lang_syntax,
doctools::idx
KEYWORDS
formatting engine, index, index formatter, keywords, markup, plugin, semantic markup
CATEGORY
Documentation tools
COPYRIGHT
Copyright (c) 2007 Andreas Kupries <andreas_kupries@users.sourceforge.net>