Re: SLOPE - Planner optimizations on monotonic expressions.

Thanks for the updated version, I didn't find more correctness issues
with the patch in v9.

> Is there a written standard/recommendation for these, maybe
> /*
> * arg0_asc_slope_support
> *
> * Prosupport: f(x, ...) is monotonically increasing in x.
> */

I think most of the function comment's don't mention the function name
at all, but those that do follow this approach with a blank line.
At some places I also see a

/* functionname: some description
*
* more description
*/

pattern.

CREATE OR REPLACE FUNCTION log10(numeric)
RETURNS numeric
LANGUAGE sql
+ SUPPORT arg0_asc_slope_support
IMMUTABLE PARALLEL SAFE STRICT COST 1
RETURN log(10, $1);

Shouldn't these additions, and generally the feature itself / how it
works / what's the contract for functions / ... have proper
documentation as it is user/extension facing?

Another similar question is if the feature should have an enable_
toggle similar to others, enable_slope?