@Override
	public Attribute resolveToAttribute(String x, String y, ActionAST node) {
		LabelElementPair anyLabelDef = getAnyLabelDef(x);
		if ( anyLabelDef!=null ) {
			if ( anyLabelDef.type==LabelType.RULE_LABEL ) {
				return g.getRule(anyLabelDef.element.getText()).resolveRetvalOrProperty(y);
			}
			else {
				AttributeDict scope = getPredefinedScope(anyLabelDef.type);
				if (scope == null) {
					return null;
				}

				return scope.get(y);
			}
		}
		return null;

	}
$x.y	Attribute: x is surrounding rule, label ref (in any alts)
tool/src/org/antlr/v4/tool/Rule.java