public CodeBlockForOuterMostAlt getOuterMostAltCodeBlock() {
		if ( this instanceof CodeBlockForOuterMostAlt ) {
			return (CodeBlockForOuterMostAlt)this;
		}
		CodeBlock p = enclosingBlock;
		while ( p!=null ) {
			if ( p instanceof CodeBlockForOuterMostAlt ) {
				return (CodeBlockForOuterMostAlt)p;
			}
			p = p.enclosingBlock;
		}
		return null;
	}
Walk upwards in model tree, looking for outer alt's code block
tool/src/org/antlr/v4/codegen/model/SrcOp.java