public boolean deleteChild(org.antlr.runtime.tree.Tree t) {
		for (int i=0; i<children.size(); i++) {
			Object c = children.get(i);
			if ( c == t ) {
				deleteChild(t.getChildIndex());
				return true;
			}
		}
		return false;
	}
Walk ancestors of this node until we find ALT with
 alt!=null or leftRecursiveAltInfo!=null. Then grab label if any.
 If not a rule element, just returns null.
tool/src/org/antlr/v4/tool/ast/GrammarAST.java