The JAXP RI fails to accept the following schema:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
<xs:simpleType name="dataType">
<xs:restriction base="xs:NCName">
<xs:pattern value="[a-z]$?[a-z]*"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>

Citing the following error:

[ERROR] InvalidRegex: Pattern value '[a-z]$?[a-z]*' is not a valid regular expression. The reported error was: 'Unexpected meta character.'.
  line 4 of file:/C:/kohsuke/Sun/JAXB/jaxb-ri/sandbox/test.xsd

Note that in the XML Schema spec, '$' is not a meta character.
See http://www.w3.org/TR/xmlschema-2/#nt-Char