[Devel] uri-map: what is the `map` parameter for?

[Gabriel Beddingfield]

Hi guys,

Had a crash with SLV2 when calling...

    UMF->uri_to_id(UMF->callback_data, // callback_data
                   0,                  // map
                   "http://lv2plug.in/ns/ext/midi#MidiEvent"); // uri

Crashing because (map == 0) is a bug, but...

Just what *is* this map parameter for?  Docs say:

* @param map The 'context' of this URI.  Certain extensions may define a
*        URI that must be passed here with certain restrictions on the
*        return value (e.g. limited range).  This value may be NULL if
*        the plugin needs an ID for a URI in general.

Which doesn't give me any clues about what it's for... so I made it 
NULL.  What I expect is a simple, global registry with URI ==> INT 
mappings, so this 'context' thing has me befuddled.

Any hints?

-gabriel