After upgrading to Flex 4.5 recently, I have become annoyed with Flash Builder's new obsession with marking metadata tags as unknown.
Unknown to you, FB, maybe, but not to me or my friends....we make heavy use of custom metadata tags, especially since adopting the parsley framework almost two years ago.
So I was kinda happy to find this after some digging:
Turns out, hidden down in the flex 4.5 sdk frameworks dir is a little file called metadata.xml that provides metadata about the metadata tags. The FB tooling uses this file to configure the new auto-prompters for metadata.
Cribbing the syntax from the SDK file, I crafted a metadata.xml for parsley 2.4 which has helped to shut FB up. It just needs to be included as an asset copied into the SWC.