This question already has an answer here:
In another question here, I saw this
poincareMetric[u_?VectorQ, v_?VectorQ] := ...
Whilst I am familiar with the syntax label_Type, e.g. x_Real, I had not seen this form, but when I tried to search the MMA documentation I found that searching for
_? returned no results and neither
? on their own suggested to me a clear meaning for
_? - especially since I would have written
1/ What does
_? actually mean, and
2/ What is this function definition doing that would not be done by e.g.
but most importantly,
3/ How does one search for help on such terse syntactic constructions effectively? (So as not to ask almost trivial questions here)