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