Option/variable bindings unavailable when evaluating p:viewport/@match

[gimsieke]

This pipeline does a directory listing of the directory that it resides in, and it is supposed to load all files whose names match the regex \.x[mps]l$:

<?xml version="1.0" encoding="UTF-8"?>
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc"
  xmlns:c="http://www.w3.org/ns/xproc-step" version="1.0">
  <p:output port="result" primary="true"/>
  <p:serialization port="result" indent="true" omit-xml-declaration="false"/>
  <p:option name="regex" select="'\.x[mps]l$'"/>
  <p:directory-list path="."/>
  <p:viewport match="c:file[matches(@name, $regex)]" name="vp">
    <p:load name="load">
      <p:with-option name="href" select="/*/@name"/>
    </p:load>
    <p:sink/>
    <p:insert match="/*" position="last-child">
      <p:input port="source">
        <p:pipe port="current" step="vp"/>
      </p:input>
      <p:input port="insertion">
        <p:pipe port="result" step="load"/>
      </p:input>
    </p:insert>
  </p:viewport>
</p:declare-step>

Morgana gives a correct result without raising an error. Calabash, on the other hand, complains:

ERROR: net.sf.saxon.trans.XPathException: Undeclared variable in XPath expression: $regex

The 1.0 spec makes it clear, in Sect. 2.6, that all bindings be available when evaluating p:viewport/@match.

Tested with XML Calabash 1.1.15-96 and 1.1.16-97.