Size limit on GiST nodes not documented

In GiST indexes, storing nodes larger than an index page is apparently
not allowed. This prohibits, for example, storing 600 entry float8
arrays in the index. For SP-GiST in PostgreSQL 9.2, it was decided
that this should be documented:

"Individual leaf tuples and inner tuples must fit on a single index
page (8KB by default)."[1]

... but for GiST indexes, this is never mentioned explicitly. The
result was that I wasted many hours developing a GiST index before
noticing it could not be used with my data.

1. http://www.postgresql.org/docs/9.2/static/spgist-implementation.html#SPGIST-LIMITS