Plug-in descriptor file

The plug-in descriptor file (plugin.xml) controls all aspects of a plug-in, making each extension visible to the rest of the toolkit. The file uses pre-defined extension points to locate changes, and then integrates those changes into the core DITA-OT code.

Validating plug-ins

DITA-OT includes a RELAX NG schema file that can be used to validate the plugin.xml files that define the capabilities of each plug-in.

To ensure the syntax of your custom plug-in is correct, include an <?xml-model?> processing instruction at the beginning of the plugin.xml file, immediately after the XML prolog:

<?xml-model href="dita-ot/plugin.rnc" type="application/relax-ng-compact-syntax"?>

If your authoring environment does not apply this schema automatically, point your editor to dita-ot-dir/resources/plugin.rnc to associate the schema with your plug-in file.

Plug-in identifiers

Every DITA-OT plug-in must have a unique identifier composed of one or more dot-delimited tokens, for example, com.example.rss. This identifier is used to identify the plug-in to the toolkit for installation, processing, and when determining plug-in dependencies.

Note: The default DITA-OT plug-ins use a reverse domain naming convention, as in org.dita.html5; this is strongly recommended to avoid plug-in naming conflicts.
Each token can include only the following characters:
  • Lower-case letters (a-z)
  • Upper-case letters (A-Z)
  • Numerals (0-9)
  • Underscores (_)
  • Hyphens (-)

<plugin>

The root element of the plugin.xml file is <plugin>, which has a required @id attribute set to the unique plug-in identifier.

Figure 1. Sample <plugin> element
<plugin id="com.example.html5-javascript">

Plug-in elements

The <plugin> element can contain the following child elements:

<extension-point>

An optional element that defines a new extension point that can be used by other DITA-OT plug-ins.

The following attributes are supported:

Attribute Description Required?
id Extension point identifier Yes
name Extension point description No

Like plug-in identifiers, extension point identifiers are composed of one or more dot-delimited tokens.

Note: Extension point identifiers should begin with the identifier of the defining plug-in and append one or more tokens, for example, org.dita.example.pre.
Figure 2. Sample <extension-point> element
<extension-point id="dita.xsl.html5" name="HTML5 XSLT import"/>
<feature>

An optional element that supplies values to a DITA-OT extension point.

The following attributes are supported:

Attribute Description Required?
extension Identifier of the DITA-OT extension point Yes
value Comma separated string value of the extension Either the @value or @file attribute must be specified
file Name and path of a file containing data for the extension point.

Depending on the extension point, this might be specified as an absolute path, a path relative to the plugin.xml file, or a path relative to the DITA-OT root.

Either the @value or @file attribute must be specified
type Type of the @value attribute No
Figure 3. Sample <feature> elements

If more than one <feature> element supplies values to the same extension point, the values are additive. For example, the following are equivalent:

<feature extension="org.dita.example.extension-point" value="a,b,c"/>
<feature extension="org.dita.example.extension-point" value="a"/>
<feature extension="org.dita.example.extension-point" value="b"/>
<feature extension="org.dita.example.extension-point" value="c"/>
<meta>

An optional element that defines metadata.

The following attributes are supported:

Attribute Description Required?
type Metadata name Yes
value Metadata value Yes
Figure 4. Sample <meta> element
<meta type="foo" value="bar"/>
<require>

An optional element that defines plug-in dependencies.

The following attributes are supported:

Attribute Description Required?
plugin The identifier of the required plug-in.

To specify alternative requirements, separate plug-in identifiers with a vertical bar.

Yes
importance Identifies whether the plug-in is required (default) or optional. DITA-OT provides a warning if a required plug-in is not available. No
Figure 5. Sample <require> element
<require plugin="org.dita.html5"/>
<template>

An optional element that defines files that should be treated as templates.

Template files can be used to integrate DITA-OT extensions. Templates typically extend the default transformation-type-specific build files via <dita:extension> elements. When the plug-in installation process runs, template files are used to recreate build files, and the specified extension points are replaced with references to the appropriate plug-ins.

The following attributes are supported:

Attribute Description Required?
file Name and path to the template file, relative to the plugin.xml file Yes
Figure 6. Sample <template> element
<template file="build_dita2html5_template.xml"/>
<transtype>

An optional element that defines a new output format (transformation type).

The following attributes are supported:

Attribute Description Required?
name Transformation name Yes
desc Transformation type description No
abstract When true, sets the transformation type as abstract, meaning it can be extended by other plug-ins, but cannot be used directly.

For example, the org.dita.base plug-in defines an abstract base transformation type that is extended by other DITA-OT plug-ins.

No
extends Specifies the name of the transformation type being extended No
Figure 7. Sample <transtype> element
<transtype name="base" abstract="true" desc="Common">
  <!-- ⋮ -->
  <param name="link-crawl" 
         desc="Specifies whether to crawl only topic links found in maps, or all discovered topic links."
         type="enum">
    <val>map</val>
    <val default="true">topic</val>
  </param>
  <!-- ⋮ -->
</transtype>

The <transtype> element may define additional parameters for the transformation type using the following child elements.

<param>

An optional element that specifies a parameter for the transformation type.

The following parameter attributes are supported:

Attribute Description Required?
name Parameter name Yes
desc Parameter description No
type Parameter type (enum, file, string) Yes
deprecated When true, identifies this parameter as deprecated No
required When true, identifies this parameter as required No
<val>

A child of <param> (when @type=enum) that specifies an enumeration value.

The following attributes are supported:

Attribute Description Required?
default When true, sets the enumeration value as the default value of the parent <param> Only for the default <val>

Any extension that is not recognized by DITA-OT is ignored. Since DITA-OT version 1.5.3, you can combine multiple extension definitions within a single plugin.xml file; in older versions, only the last extension definition was used.