Missing(?) explanation of APOC parameters

After looking at various questions posted on the forum, I have noticed that a big stumbling block for newbies is that it appears that the parameter signature notation is not explained. (At least, I haven't been able to find it.)

If the parameter signature notation page does exist, then each APOC documentation page should have a link to that page.

For example from one of the simpler APOC functions:

apoc.coll.max(values :: LIST? OF ANY?) :: (ANY?)

double colon :: isn't explained, nor ANY or the ?

As a long time programmer, I can guess what the notation is (especially after looking at the examples). However, newbies are often intimidated by this, which is unfortunate, because APOC gives Neo4J a major advantage over other DB systems. (I'm managing fine. I'm posting this for the newbies who are struggling.)