Ruben’s blog

This afternoon I found out that when you’re defining styles for the same selector in your main Flex application and in one of your modules, the latter style-declaration will not be used, at all. I’m not sure whether this is a quirk that has yet to be documented or that it’s something that has already [...]

If you have ever tried to add mx.core.ToolTip (or certain other classes) as a mxml-tag to your Flex project then you might’ve run into the following compiler-error:
“Could not resolve <mx:ToolTip> to a component implementation.”
So why does Flex (or rather MXMLC, the compiler) let you write <mx:Button> and <mx:Canvas> and all those other Flex components, but [...]