XSL:Line Numbers in text output?

[SMerrill]

I am working on an XSLT which transforms a multi-level XML into some plain text code, similar GWBASIC. I need the output to have line numbers, such as
10 ...
20 ...
30 ...
etc.
I can use

<xsl:value-of select=&quot;$LineNum&quot;>

to display a variable, the only problem is that I cannot figure out how to add 10 to it each time.
I tried

<xsl:variable name=&quot;LineNumber&quot; select=&quot;$LineNumber+10&quot; />,

but that isn't exactly working well. Thoughts?