XSLT/XPath function references

Hello all,
Am a newbie in XSLT, so please excuse this probably oft-repeated question.
I am trying to figure out all the functions that can be used in XSLT
conditional expressions (such as in select="", <xsl:when test="" etc.)

I know of the following:
1) XSLT functions(and my reference for that is
http://zvon.org/xxl/XSLTreference/Output/index.html)

2) XPath
   2.1) http://www.caucho.com/products/resin/ref/xpath.xtp and
   2.2) http://www.caucho.com/products/resin/ref/xpath-fun.xtp)

3) And the most commonly used quick reference from MulberryTech (I have the
pdf file locally stored on my PC)

Questions:
1) When and for what are 1 and 2 usually used for? Moreover, what is the
difference between 2.1 and 2.2
2) Are there constraints as to where each of these can and cannot be used?
Any tutorial on this would suffice. I will dig in into the details.

Thanks much. I appreciate your time.
Best regards,
--KH


 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list