


docidx_plugin_apiref(n)Documentation toolsdocidx_plugin_apiref(n)


______________________________________________________________________________

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.




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       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  lan-
       guage  itself  should  start  with the docidx language introduction and
       proceed from there to the formal specifications, i.e. the  docidx  lan-
       guage 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 sec-
       tion 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 pro-
       cessor, 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  textu-
       til::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 out-
              put in place of the symbolic filename symfname. It  will  return
              the  unchanged input if no mapping was established for symfname.




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              The required mappings are established with the method map  of  a
              frontend, as explained in section OBJECT METHODS of the documen-
              tation 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 what-
              ever 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  direc-
              tory causes an error.

       dt_source file
              Controlled filesystem access. This command allows the index for-
              matting engine to load additional Tcl code it  may  need.   Only
              files  which  are  either in the same directory as the file con-
              taining 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  con-
              text  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



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              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  fron-
       tend 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 estab-
       lished 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 parame-
       ters  is  established,  followed  by calls setting the parameters. That
       second part is optional.



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       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:

       o      First some basic parameters are determined.

       o      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.

       o      Embedded within each run we have one or more passes, each start-
              ing 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  begin-
              ning  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.  immedi-
              ately  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.




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       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 doc-
              ument. 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 inter-
              nal 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  consid-
              ered 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  pro-
       cessed  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.



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       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 lan-
       guage 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,  will  undoubtedly  contain  bugs  and  other  problems.
       Please  report  such in the category doctools of the Tcllib SF Trackers
       [http://sourceforge.net/tracker/?group_id=12883].  Please  also  report
       any ideas for enhancements you may have.

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>










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