checck if external xml is valid with xsl/javascript?

Hi

I have the following in my xsl:

<xsl:for-each select="document($vacature_url)//vacature">

However, since this external xml is not in our control sometimes its not
valid and screws up the rest of the page.

Can I check from within my xsl file if the external xml is valid and
based on that either run the  for each or skip it?

Thanks

Armand

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