DispatchQ
A Curiosity: What is DispatchQ?
DispatchQ returns True if applied to a Dispatch object, so it is useful for identifying Dispatch objects.
Mathematica autofill shows the function DispatchQ. It does not appear in the Mathematica Documentation Center. Except for the question linked above, a search for DispatchQ on the Mathematica Stack Exchange comes up with nothing, and a Google search for "DispatchQ" reveals nothing relating to Mathematica.
Compile`SetIterate
What Does Compile`SetIterate Do?
Compile`SetIterate sets an iterator.
The list of compilable functions (given by Compile`CompilerFunctions[] // Sort) shows Compile`SetIterate. It does not appear in the Mathematica Documentation Center. Moreover, except for the question linked above and for references to merely the list of compilable functions, a search for Compile`SetIterate on the Mathematica Stack Exchange comes up with nothing and a Google search for Compile`SetIterate reveals nothing I can see relating to Mathematica.