Test 
         p:viewport with  matched text.
Test ab-viewport-015.xml is expected to pass.
<p:declare-step xmlns:p="http://www.w3.org/ns/xproc" version="3.0">
   <p:output port="result">
   <p:viewport match="para/text()">
      <p:with-input>
         <doc>
            <para>Replace me</para>
         </doc>
      </p:with-input>
      <p:identity>
         <p:with-input port="source">
            <replaced/>
         </p:with-input>
      </p:identity>
   </p:viewport>
</p:declare-step>
<s:schema xmlns="http://www.w3.org/1999/xhtml" xmlns:s="http://purl.oclc.org/dsdl/schematron" queryBinding="xslt2">
   <s:pattern>
      <s:rule context="/">
         <s:assert test="doc">The document root is not 'doc'.</s:assert>
         <s:assert test="doc/para/replaced">Element para does not have chuld 'replaced'.</s:assert>
         <s:assert test="count(doc/para/text())=0">Element para should not have text children.</s:assert>
      </s:rule>
   </s:pattern>
</s:schema>
Added attribute 'queryBinding' to schematron's schema.
Additional tests for p:viewport (partly ported from 1.0)