The Metadata tag is used to describe the SWF movie in a robot readable form. It will be used by search engines to index your Flash movies.
The f_metadata string is an XML buffer defined using the RDF definition compliant with the XMP specification. You can find more information on the W3C and other websites:
Note that this description can describe everything, from the entire movie to each single line of code in your action scripts.
The string must be UTF-8 encoded.