@Override
    public void visitMembers(ObjectVisitor visitor) {
        super.visitMembers(visitor);
        visitor.visit("attribute", attribute);
    }
Sets the name of the attribute whose value we do lookup in.

@param attribute The attribute to retrieve.
@return This, to allow chaining.
searchlib/src/main/java/com/yahoo/searchlib/expression/InterpolatedLookupNode.java