The access an expression reads, when that is all it does: a variable, or a chain of SUBJECT / PREDICATE / OBJECT around one.
SUBJECT
PREDICATE
OBJECT
The expression to read
The positions collected so far, filled in by the recursion
the access, or undefined when the expression does more than read one
undefined
The access an expression reads, when that is all it does: a variable, or a chain of
SUBJECT/PREDICATE/OBJECTaround one.