The internal function mousetrap_get_next_id starts at the first number after the last reserved identifier(MT_RESERVED_LAST) in this enum. If you wish to use your own identifier generation scheme, identifiers less than or equal to MT_RESERVED_LAST will cause undesirable results.
MT_TRANSPARENCY | Used to denote transparency information in a mousetrap. |
MT_PLACEHOLDER | Used for arbitrary things. Mostly internal, but also a failure value from mousetrap_lookup_id. |
MT_RESERVED_LAST | Included to make client code work easily when/if more reserved IDs are added to the system. |