Documentation for V function

Question

Hi Folks,
Sprinkled throughout lots of the documentation there is a reference to the "v()" function.
Examples include "v('APP_USER')" and similar.
Since this function doesn't appear to be part of a PL/SQL package, using it perturbs me slightly: I always
like to have at least some sort of grasp of what I'm using and although I am grateful for all the folk that
show examples of its use, there's nothing like having the fundamental definition to make a Developer sleep
a little easier at night... :-)
Can any kind soul give a URL for the place in the documentation where it describes this mysterious function
please?
Thanks in advance
Mungo

Answer 1

Thanks to (currently) the two respondents. Though I didn't state it, it was the API documentation that I
was seeking, hence I marked "jarola" as Correct. The other respondent was most helpful too.
Follow-on question: if I use "v(...)" in a database table trigger, that trigger runs in the database and (I think) only has
access to the schema's code as well as the usual built-ins.
Since this function belongs to Apex, how is it "attached" to my schema? When I specify a schema to be linked to a Workspace,
is this where the linking occurs?
Hoping you can see my question through the fog of feeble words I've used; thanks in advance.
Mungo