> to clarify my request, suppose I don't have needed sequence 
> of nodes anywhere, and want to access every 4 elements: 1, 5, 
> 9, ... to the end. Do I have to use <xsl:if test="position() 
> mod 4 = 1", or there is a more flexible way?

In what way do you consider the solution inflexible? Obviously you can
replace either number by a variable. 

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