afs:header describes the context of the query. It can have up to five child elements. All elements are optional, and may only occur once in the reply feed. They have the following semantic:
- afs:query gives information about the query (keywords, filters, etc.).
- afs:user gives information about the user environment (browser, IP address, etc.). Sub node afs:output gives information about format, encoding, and character set of the query.
- afs:performance specifies the all-inclusive duration of the query, measured in milliseconds from the reception of the query to the delivery of the output feed.
- afs:explain gives additional information produced by afs:explain query parameters.
- afs:error lists error messages describing problems encountered while processing the query.