I had to use a variable in an xslt template. The value for that variable would be returned by a stored procedure at a SQL Server DB. So, I decided to populate the variable with static content:
<xsl:variable name="hideColumns" select ="'ISBN,author_id,vendor_id'" />
Populated with the static content, the variable proved to be a good replacement for the real-life data. So, as soon as the stored procedure was deployed, my xslt template was readily updated with the appropriate select statement in the hideColumns variable declaration.