Prefilters 1) They are useful to introduce custom dataTypes (see ajax/jsonp.js for an example) 2) These are called: - BEFORE asking for a transport - AFTER param serialization (s.data is a string if s.processData is true) 3) key is the dataType 4) the catchall symbol "" can be used 5) execution will start with transport dataType and THEN continue down to "" if needed
