Hi Hackers,
A user on IRC was confused about how to delete a security label using
the `SECURITY LABLEL ON … IS …` command, and looking at the docs I can
see why.
The synopsis just says `IS 'label'`, which implies that it can only be a
string. It's not until you read the description for `label` that you
see "or `NULL` to drop the security label." I propose making the
synopsis say `IS { 'label' | NULL }` to make it clear that it can be
NULL as well. The same applies to `COMMENT ON … IS …`, which I've also
changed similarly in the attached.
- ilmari