[xsl] Priorities of unionised patterns

[Ihe Onwuka <ihe.onwuka@xxxxxxxxx>]

Given that the sub parts of a unionized pattern retain their individual
priorities

<xsl:template match="A|B[*] ......

What should be the semantic if you were to now specify a priority attribute.
The instinctive reaction would be they should all get the same priority but
 there not a case for saying that it should not be allowed.

The rationale would be to highlight that the subparts may have had
different priorities in the first place so making their priorities
homogenous might actually be the source of what would be a hard to find bug.