The apply-templates keyword instructs the XSLT to recursively process any the children of the source element.
using | an (optional) XPath expression indicating the node and children to match. |
scope | the (optional) scope (mode) of this template, matching that defined in an match statement. |
<with> | an (optional) parameter carried into the invoked match templates via a with. |
<sort> | the (optional) definition of how the match templates should be applied and sorted. |
This says that when any list is detected then the children of "//list" are processed with a parameter param-1 with a value of "'List Title'" (a simple string), and the results of applying the templates sorted with the <a> element in descending order.
Note that if the "descending" instruction had been "ascending" or omitted then this is the default value and the "order" attribute would be also omitted in the output XSLT.
As an aside the above can also be written, with the same effect, as
A simple misspelling.
will give the error
An illegal or misspelled keyword on the following line
will give a similar error