Member predicate AssignSubExpr :: getAPrimaryQlClass
Gets the name of a primary CodeQL class to which this element belongs.
For most elements, this is simply the most precise syntactic category to
which they belong; for example,
AddExpr is a primary class, but
BinaryExpr is not.
This predicate always has a result. If no primary class can be
determined, the result is
"???". If multiple primary classes match,
this predicate can have multiple results.