1.5. Element `transform`
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### 1.5. Element `transform`

    <transform
      stylesheet = anyURI
      cacheStylesheet = boolean : false
      file = Path
      to = Path
    >
      Content: [ parameter | parameterGroup ]*
    </transform>

    <parameter
      name = Non empty token
    >
      Content: Parameter value
    </parameter>

    <parameterGroup
      name = Non empty token
    />

Converts a XML file to another format using built-in XSLT engine.

Attributes:

stylesheet

  Specifies which XSLT style sheet to use. If this URL is relative, it is relative to the directory containing the XXE configuration file.

  The URI specified in this attribute may be also resolved using XML catalogs.

cacheStylesheet

  If this attribute is specified as `true`, a precompiled form of the XSLT style sheet is built and then cached for subsequent uses.

  It is not recommended to cache an XSLT style sheet unless this style sheet is small and used in highly interactive process commands (like in example 1 below).

file

  Input file.

to

  Output file.

`Parameter` and/or named `parameterGroup` child elements are used to parametrize the XSLT style sheet. Example: `<parameter name="paper.type">A4</parameter>`.

These parameters are described in the documentation of the XSLT style sheets:

- See DocBook XSL Stylesheet Documentation.

- See The Slides Document Type.

If a `transform` element references a `parameterGroup`, this means that a `parameterGroup` configuration element (see Section 17, “parameterGroup” in XMLmind XML Editor - Configuration and Deployment) with the same name is defined elsewhere in this configuration file or in another configuration file. However, it is not an error to reference a `parameterGroup` for which the configuration element is not found.

#### 1.5.1. Using a custom XSLT style sheet

A user can force the use of a custom style sheet of his own instead of the one normally specified in attribute `stylesheet`.

In order to do this, the user needs to specify a property called ``process_command_name`.transform` in any XXE configuration file. The value of this property must be the URL of the custom XSLT style sheet. (This property is typically specified in the user's `customize.xxe` file. See `property` configuration element in Section 16, “property” in XMLmind XML Editor - Configuration and Deployment.)

If a `process` command has several `transform` child elements, property ``process_command_name`.transform` specifies a style sheet for the first `transform`, ``process_command_name`.transform.2` specifies a style sheet for the second `transform`, ``process_command_name`.transform.3` specifies a style sheet for the third `transform` and so on.

Example: the process command to be customized is called `docb.toPS` (see ``XXE_install_dir`/addon/config/docbook/xslMenu.incl`). User has added the following property to his `customize.xxe` file.

    <property name="docb.toPS.transform" url="true">fo_docbook.xsl</property>

Note that the URL is relative to the configuration file containing the definition of property `docb.toPS.transform` (here, it is relative to `customize.xxe`).

The custom XSLT style sheet `fo_docbook.xsl` contains:

    <?xml version='1.0'?>
    <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                    xmlns:fo="http://www.w3.org/1999/XSL/Format"
                    version='1.0'>

    <xsl:import href="xxe-config:docbook/xsl/fo/docbook.xsl"/>

    <xsl:template match="bookinfo/author|info/author" mode="titlepage.mode">
      <fo:block>
        <xsl:call-template name="anchor"/>
        <xsl:call-template name="person.name"/>
        <xsl:if test="affiliation/orgname">
          <fo:block>
            <xsl:apply-templates select="affiliation/orgname"
                                 mode="titlepage.mode"/>
          </fo:block>
        </xsl:if>
        <xsl:if test="email|affiliation/address/email">
          <fo:block>
            <xsl:apply-templates select="(email|affiliation/address/email)[1]"/>
          </fo:block>
        </xsl:if>
      </fo:block>
    </xsl:template>

    </xsl:stylesheet>

Note how the stock `docbook.xsl` is imported by this customized version.

### Tip

In our opinion, it is almost impossible to cope with the complexity of customizing Norman Walsh's DocBook XSLT style sheets without reading this excellent book: DocBook XSL: The Complete Guide by Bob Stayton.

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