The "/builtin" page:
Return one of many built-in content files.  Query parameters:
- name=FILENAME
 - Return the single file whose name is FILENAME.
 - mimetype=TYPE
 - Override the mimetype in the returned file to be TYPE. If this query parameter is omitted (the usual case) then the mimetype is inferred from the suffix on FILENAME
 - m=IDLIST
 - IDLIST is a comma-separated list of integers that specify multiple javascript files to be concatenated and returned all at once.
 - id=UNIQUEID
 - Version number of the "builtin" files. Used for cache control only.
 
At least one of the name= or m= query parameters must be present.
If the id= query parameter is present, then Fossil assumes that the result is immutable and sets a very large cache retention time (1 year).