<xsl:analyze-string select="concat($str, ',')" regex='(("[^"]*")+|[^,]*),'>
    <xsl:matching-substring>
      <xsl:sequence select='replace(regex-group(1), "^""|""$|("")""", "$1")'/>
    </xsl:matching-substring>
  </xsl:analyze-string>

Here you have regex='...' and select='...' ; but your HTML page shows
regex="..." and select="..." ; which is invalid XML given the quotes
in the regular expression.

I had copied the code out of the webpage and saxon won't compile it.
I modified the quotes and all workes perfectly!

Thx,
--
Rodman