XML, adding booleans

Hay /prog/ I'm new to using XML, and it sucks.  But that's neither here nor there.  My question is, is there any way to add boolean values together in it?

For example, <xsl:value-of select="Some/Thing [@id = '7'] != '' + Some/Thing/Else !=''" /> to get a 2, 1 or 0.

You are confused. XML doesn't do any computions. XML is used only to markup data. To do what you want, you would need a programming language that uses XML grammar. I'm not sure any exists at the moment.