3. Modularization support in document description languages

Today's description languages can support modularization functionalities.

3.1 Structure description

RELAX NG[3], [4], for example, can support modularity.

Referencing external patterns:
The external pattern can be used to reference a pattern defined in a separate file. The external keyword is followed by a quoted string specifying the URL of a file containing the pattern. The external pattern matches if the pattern contained in the specified URL matches.

In addition, RELAX NG has the features of
- Combining definitions
- Merging grammars
- Replacing definitions

3.2 Style specification

XSLT provides two mechanisms to combine stylesheets:
- <xsl:include href = uri-reference /> an inclusion mechanism that allows stylesheets to be combined without changing the semantics of the stylesheets being combined, and
- <xsl:import href = uri-reference /> an import mechanism that allows stylesheets to override each other.