is Node At
Returns true if the child at index is a node (excluding TokenNode).
Return
true if the child is a node, false otherwise
Parameters
index
The zero-based index of the child
Returns true if the child at index is a node that satisfies the predicate.
Return
true if the child is a node and satisfies the predicate, false otherwise
Parameters
index
The zero-based index of the child
predicate
A function that tests the node