Flash Builder 4.5 added code completion for metadata tags. Adding support for custom metadata tags however requires building a swc containing a metadata.xml file outlined in hard to find documentation. They could have just added a preferences panel but this is a good way for developers to include custom metadata info right in their library swcs.
Two libraries I use quite often and leverage metadata tags heavily are Parsley and FlexXB. Neither of them have included this metadata.xml file in their latest releases so I have created 2 extra swcs containing just the metadata info using xml files found here and here respectively. I'm sharing them here in case anyone else wants to use them.
Note that they just contain the metadata info not the rest of the library. I could have bundled it in, but if the library recieves an update that still doesn't include the metadata file it will need to be integrated again.