The FreeBSD manpage to HTML CGI script expects a query string with 2 parameters.  The first, query, is the name of the man page; in other words, the contents of the refentrytitle element.  The second parameter, sektion (yes, with that spelling, the author of the script is German) is equivalent to the contents of the manvolnum element.  All we have to do is write a function that can turn these two pieces of information in to the URL.
	This is quite a simple function to write.  However, I’ve made it a little more complex to try and be a bit more futureproof.  It would be simple to write a function that took two strings as arguments and pasted them in to the URL.  However, suppose you then want to extend this function to do something else (I’ll give an example of ‘something else’ later on).  If the function needed any more information to do its job you would have to not only rewrite this function, but you would also need to rewrite the citerefentry code in layer-2.dsl (which might cause problems for any other customisations built on top of it).
	So, instead, this function takes a node as its argument (conceptually, you can think of the node as being the current element that’s being processed).  If no node is passed in then the function works out what the current node is, and uses that instead.
	The first line of the function deals with the argument passing, and calls the node it’s using “n”.  Remember, we expect “n” to correspond to the citerefentry element we’re currently dealing with.
	We set up two variables; “r” is the node (or element) that corresponds with the refentrytitle that is a child of “n”.  Similarly, “m” corresponds to the manvolnum node.
	Then all we do is construct a string, using string-append.  You can see that the string is a combination of static strings, and the contents of the “r” and “m” nodes, where the contents of a node are extracted by the “data” function.
	Simple eh?