Provided by: tcllib_1.17-dfsg-1_all 
NAME
doctools_plugin_apiref - doctools plugin API reference
SYNOPSIS
dt_copyright
dt_file
dt_mainfile
dt_fileid
dt_fmap symfname
dt_format
dt_imgdata key extensions
dt_imgdst key extensions
dt_imgsrc key extensions
dt_lnesting
dt_module
dt_read file
dt_source file
dt_user
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?
fmt_initialize
fmt_listvariables
fmt_numpasses
fmt_postprocess text
fmt_setup n
fmt_shutdown
fmt_varset varname text
fmt_plain_text text
_________________________________________________________________________________________________
DESCRIPTION
This document is intended for plugin writers, i.e. developers wishing to write a doctools
formatting engine for some output format X.
It specifies the interaction between the doctools package and its plugins, i.e. the
interface any doctools 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 doctools language introduction and proceed from there to the formal
specifications, i.e. the doctools language syntax and the doctools language command
reference.
OVERVIEW
The API for a doctools 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
doctools formatting engine, is able to query the frontend. These commands are provided by
the frontend and linked into the plugin interpreter.
I.e. a doctools 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_copyright
Query command. It returns a string containing the copyright information the
doctools processor was configured with. The relevant option is -copyright).
dt_file
Query command. It returns the full path of the file containing the input currently
processed by the engine. This may be an included file.
dt_mainfile
Query command. It returns the full path of the toplevel file containing the input
currently processed by the engine.
dt_fileid
Query command. It returns the name of the file containing the input currently
processed by the engine, without path, nor extension.
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.
dt_format
Query command. It returns the name of the format associated with the doctools
formatting engine.
dt_imgdata key extensions
Query command. Access to the image map. Looks for an image recorded under the key
and having on the specified extension. If a matching image is found its data is
returned as the result of the command. Otherwise an empty string is returned.
dt_imgdst key extensions
Query command. Access to the image map. Looks for an image recorded under the key
and having on the specified extension. If a matching image is found its destination
path in the output is returned as the result of the command. Otherwise an empty
string is returned.
dt_imgsrc key extensions
Query command. Access to the image map. Looks for an image recorded under the key
and having on the specified extension. If a matching image is found its origin path
is returned as the result of the command. Otherwise an empty string is returned.
dt_lnesting
Query command. It returns the number of lists currently open.
dt_module
Query command. It returns the name of the module the input currently processed
belongs to.
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 doctools 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.
dt_user
Query command. It returns the name of the current user as known to the tcl
interpreter the frontend controlling the formatting engine resides in.
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:
fmt_numpasses -> n
fmt_listvariables -> vars
fmt_varset var1 value1
fmt_varset var2 value2
...
fmt_varset varK valueK
fmt_initialize
fmt_setup 1
...
fmt_setup 2
...
...
fmt_setup n
...
fmt_postprocess
fmt_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 fmt_varset.
In each of the passes, i.e. after the calls of fmt_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 doctools markup
language, as specified in the doctools language syntax specification.
A different way of looking at the sequence is:
• First some basic parameters are determined.
• Then everything starting at the first fmt_varset to fmt_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 fmt_setup
and going until either the next fmt_setup or fmt_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:
fmt_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.
fmt_listvariables
Initialization/Shutdown and Engine parameters. Second command is called after the
plugin code has been loaded, i.e. immediately after fmt_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.
fmt_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.
fmt_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.
fmt_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.
fmt_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.
fmt_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 fmt_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 doctools 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 49 markup commands specified in the doctools 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 doctools 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 doctools markup language, as specified in
the doctools 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
doctools, doctools_intro, doctools_lang_cmdref, doctools_lang_faq, doctools_lang_intro,
doctools_lang_syntax
KEYWORDS
document, formatter, formatting engine, manpage, markup, semantic markup
CATEGORY
Documentation tools
COPYRIGHT
Copyright (c) 2007-2010 Andreas Kupries <andreas_kupries@users.sourceforge.net>