A AST node. Nodes are indexable by their types. When generating, the SUBRULES called should be located within the current location range.
Location undefined means the node does have a string representation, but it was not clarified. This happens when an AST node is patched by a client of the lib.
Optional
A AST node. Nodes are indexable by their types. When generating, the SUBRULES called should be located within the current location range.