The meaning of the first three optional parameters is exactly the same
as in the Allow command.
When processing a document with the URL
pattern, indexer downloads only a
little part of the document and tries to find
MP3 tags in it.
On success, indexer parses MP3 tags, otherwise it downloads
the rest of the document and parses it as usual, according
Content-Type HTTP response header.
CheckMP3 works only with servers
supporting HTTP/1.1 protocol.
It uses the "Range: bytes" HTTP request header
to download MP3 tags.
Indexing MP3 files is explained in details in
the Section called Creating an MP3 search engine
in Chapter 4.