Hi, simple!
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xmlns:xs="http://www.w3.org/2001/XMLSchema" exclude-result-prefixes="xs" version="2.0">
<xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>
<xsl:template match="/">
<aliases>
<xsl:for-each select="tokenize(substring-after(GBSeq_definition,'AltName:'),';')">
<xsl:for-each select="tokenize(.,'=')">
<xsl:if test="position() > 1">
<xsl:value-of select="normalize-space(.)"/>
<xsl:text>;
</xsl:text>
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</aliases>
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</xsl:stylesheet>
Cheers, John Bampton.