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# doctools::idx::export::json(n) 0.1 tcllib "Documentation tools"

## Name

doctools::idx::export::json - JSON export plugin

## Synopsis

- package require Tcl 8.4
- package require doctools::idx::export::json ?0.1?
- package require textutil::adjust

- export serial configuration

## Description

This package implements the doctools keyword index export plugin for the generation of JSON markup.

This is an internal package of doctools, for use by the higher level management packages handling keyword indices, especially doctools::idx::export, the export manager.

Using it from a regular interpreter is possible, however only with contortions, and is not recommended. The proper way to use this functionality is through the package doctools::idx::export and the export manager objects it provides.

## API

The API provided by this package satisfies the specification of the docidx export plugin API version 2.

export serial configuration

  This command takes the canonical serialization of a keyword index, as specified in section Keyword index serialization format, and contained in serial, the configuration, a dictionary, and generates JSON markup encoding the index. The created string is then returned as the result of the command.

## JSON notation of keyword indices

The JSON format used for keyword indices is a direct translation of the Keyword index serialization format, mapping Tcl dictionaries as JSON objects and Tcl lists as JSON arrays. For example, the Tcl serialization

    doctools::idx {
    	label {Keyword Index}
    	keywords {
    		changelog  {changelog.man cvs.man}
    		conversion {doctools.man docidx.man doctoc.man apps/dtplite.man mpexpand.man}
    		cvs        cvs.man
    	}
    	references {
    		apps/dtplite.man {manpage dtplite}
    		changelog.man    {manpage doctools::changelog}
    		cvs.man          {manpage doctools::cvs}
    		docidx.man       {manpage doctools::idx}
    		doctoc.man       {manpage doctools::toc}
    		doctools.man     {manpage doctools}
    		mpexpand.man     {manpage mpexpand}
    	}
    	title {}
    }

is equivalent to the JSON string

    {
        "doctools::idx" : {
            "label"      : "Keyword Index",
            "keywords"   : {
                "changelog"  : ["changelog.man","cvs.man"],
                "conversion" : ["doctools.man","docidx.man","doctoc.man","apps\/dtplite.man","mpexpand.man"],
                "cvs"        : ["cvs.man"],
            },
            "references" : {
                "apps\/dtplite.man" : ["manpage","dtplite"],
                "changelog.man"     : ["manpage","doctools::changelog"],
                "cvs.man"           : ["manpage","doctools::cvs"],
                "docidx.man"        : ["manpage","doctools::idx"],
                "doctoc.man"        : ["manpage","doctools::toc"],
                "doctools.man"      : ["manpage","doctools"],
                "mpexpand.man"      : ["manpage","mpexpand"]
            },
            "title"      : ""
        }
    }

## Configuration

The JSON export plugin recognizes the following configuration variables and changes its behaviour as they specify.

boolean indented

  If this flag is set the plugin will break the generated JSON code across lines and indent it according to its inner structure, with each key of a dictionary on a separate line.

  If this flag is not set (the default), the whole JSON object will be written on a single line, with minimum spacing between all elements.

boolean aligned

  If this flag is set the generator ensures that the values for the keys in a dictionary are vertically aligned with each other, for a nice table effect. To make this work this also implies that indented is set.

  If this flag is not set (the default), the output is formatted as per the value of indented, without trying to align the values for dictionary keys.

Note that this plugin ignores the standard configuration variables user, format, file, and map and their values.

## Keyword index serialization format

Here we specify the format used by the doctools v2 packages to serialize keyword indices as immutable values for transport, comparison, etc.

We distinguish between regular and canonical serializations. While a keyword index may have more than one regular serialization only exactly one of them will be canonical.

regular serialization

  1. An index serialization is a nested Tcl dictionary.

  2. This dictionary holds a single key, doctools::idx, and its value. This value holds the contents of the index.

  3. The contents of the index are a Tcl dictionary holding the title of the index, a label, and the keywords and references. The relevant keys and their values are

     title

       The value is a string containing the title of the index.

     label

       The value is a string containing a label for the index.

     keywords

       The value is a Tcl dictionary, using the keywords known to the index as keys. The associated values are lists containing the identifiers of the references associated with that particular keyword.

       Any reference identifier used in these lists has to exist as a key in the references dictionary, see the next item for its definition.

     references

       The value is a Tcl dictionary, using the identifiers for the references known to the index as keys. The associated values are 2-element lists containing the type and label of the reference, in this order.

       Any key here has to be associated with at least one keyword, i.e. occur in at least one of the reference lists which are the values in the keywords dictionary, see previous item for its definition.

  4. The type of a reference can be one of two values,

     manpage

       The identifier of the reference is interpreted as symbolic file name, refering to one of the documents the index was made for.

     url

       The identifier of the reference is interpreted as an url, refering to some external location, like a website, etc.

canonical serialization

  The canonical serialization of a keyword index has the format as specified in the previous item, and then additionally satisfies the constraints below, which make it unique among all the possible serializations of the keyword index.

  1. The keys found in all the nested Tcl dictionaries are sorted in ascending dictionary order, as generated by Tcl's builtin command lsort -increasing -dict.

  2. The references listed for each keyword of the index, if any, are listed in ascending dictionary order of their labels, as generated by Tcl's builtin command lsort -increasing -dict.

## 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. Please also report any ideas for enhancements you may have for either package and/or documentation.

## Keywords

JSON, doctools, export, index, serialization

## Category

Text formatter plugin

## Copyright

Copyright © 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>