[relax-ng-comment] A lightweight include mechanism

[pwilson@gorge.net (Peter Wilson)]

I am trying to code the Mozilla XUL syntax into a Relax NG schema.

One problem is the use of the <template> mechanism in XUL
http://www.mozilla.org/docs/xul/xulnotes/template-primer.html .
A <template> can be used almost anywhere in XUL to control generation of
the interface from an RDF datasource.
Given a valid <widget> definition, the <template> pattern can be
interposed into that definition. This is similar to the xhtml <table>
example in the Relax NG tutorial - but much more general.

The problem, if I understand it correctly, is that the nested grammar
idiom uses the <include> mechanism with attendant copying of the
included definitions. This is completely impractical for the XUL
<template> - the multiplication factor would be huge.

What I am suggesting is a parameterized <ref> mechanism which would
allow definitions to sandwich themselves into other definitions without
the need for copying - a sort of pattern subroutine.

1. Define a parameterized pattern (possibly included - but only once).
<define name="foo">
    <parameter name="p1"/> <!-- not strictly necessary, the use of
parameterName on a ref element is sufficient-->
    ....
    <ref parameterName="p1"/>
    ....
</define>

2. use the pattern, supplying bar as the instance of p1 to use in this
case:
<define name="bar">
    ...
    <ref name="foo">
        <parameter name="p1">bar</parameter>
    </ref>
    ....
</define>

3. the supplied parameter pattern:
<define name="bar">
...
</define>