+Additionally, a *match* stanza may contain any of the following,
+optional lines:
+
+*set* 'HEADER' 'VALUE'::
+
+ If the *match* stanza as a whole matches, the named HTTP
+ 'HEADER' in the request is set to 'VALUE' before passing the
+ request on to the specified handler. A *match* stanza may
+ contain any number of *set* lines.
+
+*xset* 'HEADER' 'VALUE'::
+
+ *xset* does exactly the same thing as *set*, except that
+ 'HEADER' is automatically prepended with the `X-Ash-`
+ prefix. The intention is only to make configuration files
+ look nicer in this very common case.