XMI.header
and XMI.exporter
are just ordinary XML tag names. Within the ASCII range the initial character has to be alphanumeric or an underscore, but after that the name can include full-stops and hyphens. So just
<xsl:template match="XMI.header">
will work for you.
The UML
names are slightly different becuase UML
is a namespace and must be declared at the top of your XSLT stylesheet. So you need
<xsl:stylesheet version="1.0"
xmlns:UML="org.omg.xmi.namespace.UML"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
after which you can just use the name as it stands, like
<xsl:template match="UML:Multiplicity">