Re: check the type of the $pattern argument to a regul

This is one way to way check if a pattern is valid:

<xsl:stylesheet version="2.0"
    xmlns:regex="java.util.regex.Pattern"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:saxon="http://saxon.sf.net/">

<xsl:template match="/">
    <xsl:value-of select="saxon:try(regex:compile(']['), 'false')"/>
</xsl:template>

</xsl:stylesheet>

This attempts to compile the regex using Java, and catches the
PatternSyntaxException using Saxon SA's saxon:try() function.  In this
case it returns "false" because "][" is invalid.

Cheers,
-- Abel Braaksma