> Once I use the <xsl:apply-templates> to a particular node in 
> the document (like <section> you have mentioned below), is it 
> possible to revert back to the earlier situation before 
> applying <xsl:apply-templates> ?

Not sure I entirely understand the question. But the context (e.g the
context node) on return from apply-templates is exactly the same as the
context before. Any instruction (such as xsl:value-of or xsl:for-each) that
appears after the apply-templates will give exactly the same result as if it
appeared before it.
> 
> What I understand by using <xsl:apply-template> means 
> filtering the nodes in XML document four output?

Not really filtering. Apply-templates selects a set of nodes (by default,
the children of the current node), and for each of them, it finds the best
matching template rule, and executes that template rule with the selected
node as the current node. Of course, if you have a template rule that does
nothing, then you have effectively filtered out the nodes that it matches.

Michael Kay
http://www.saxonica.com/