I want to create a custom mxml component that extends another mxml component. Bacially I want structure like Group -> BaseMXMLComponent -> MyMXMLComponent. I understand that it used to be the case that trying to add child component to MyMXMLComponent would throw "Error: Multiple sets of visual children have been specified for this component (base component definition and derived component definition)." error. But i've been reading few articles that says this has been fixed in Flex 4.
My question is.. is it an actually fixed, documented, and supported behavior of Flex 4? or just an undefined behavior that appears to be "fixed" but can change on future update?