Can Schematron validate XML processing instructions?

Can Schematron validate XML processing instructions?

Here is a rule for disallowing processing instructions from a document

<sch:rule context="processing-instruction()">

   <sch:report test="true()">

  There should be no processing instructions

   <sch:report>

</sch:rule>

Here is a pattern for validating that the only processing instruction allowed that starts with "xml" is "xml-stylesheet".

<sch:pattern>
<sch:rule context="processing-instruction('xml-stylesheet')">
   <sch:assert test="true()">
   The xml-stylesheet PI is allowed
    <sch:assert>
</sch:rule>
<sch:rule context=
    "processing-instruction()[starts-with(name(), 'xml')]">
   <sch:report test="true()">
   There should be no processing instructions
    that starts with 'xml' (except for xml-stylesheet)<sch:report>
</sch:rule>
</sch:pattern>

In general, validating processing instructions is no more difficult than validating element or attribute content. (This assumes your processing instruction uses a target, as is good XML practice.) The gotcha is of course that sometimes PIs contain pseudo attributes which may then have to be parsed, which can be too hard for Schematron validation.