What exactly does lanispl mean?

The field pg_language.lanispl seems to have several different meanings:

1. This is a user-defined language.

2. This language may be dropped.

3. You may define a trigger using a function defined in this language (or
in C or in internal).

4. Functions defined in this language may be called. (see fmgr.c)

5. This language needs to be dumped.

(1) and (2) are now taken care of by the new dependency system. (3)
seems to aim at disallowing trigger functions in SQL. Perhaps this should
be made explicit instead of taking this backdoor approach. I don't
understand what (4) is intending to do. (5) is not really needed if we
take pg_dump's current approach of associating a language with the
namespace of the underlying function.

Does anyone have any knowledge about this attribute? Can it be removed?

--
Peter Eisentraut peter_e(at)gmx(dot)net