Question

I’m taking an XML class online and I’m not entirely sure what the “$” is used for.

Specifically, here is a block from the text book..

<xsl:value-of select="key('agentID', $aID)" />

The dollar sign in front of aID is where I am confused. Why does it need to be there?

Answer 1

This is actually an XPath rule — thus it can be used in any XPath expression inside XSLT code.

The $ character is used as the first character in a variable (or parameter) reference within an XPath expression.

Thus:

$person

means: the xsl variable or parameter named person.

If we use just:

person

this means something completely different: all children of the context node that are named person

Forgetting the $ before the variable name in a variable reference is one of the most frequent mistakes comited by XSLT programmers.

It is a good practice to use such names for variables or parameters, that visually indicate that the named object is a variable/parameter.

For example, I always prefix the name of a variable with v and the name of the parameter with p:

$vPerson

$pTable