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
<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.