Patterns in this directory are weak in the sense that:

(1) they will very likely match things they are not intended to.  
(2) they are likely to miss a large fraction of things they should match
or
(3) they are too slow

Some protocols just don't have much to latch on to.  It is recommended
that you match on port number for these protocols.  You could use the
patterns to verify that traffic on port X really is what is expected
there.  That is, you should do:

If ( on port 4200-4700 && looks like eDonkey2000 )
	treat as eDonkey2000;

But NOT simply:

If ( looks like eDonkey2000 )
	treat as eDonkey2000;

Actually, this is fairly good advice for most Internet standard protocols
too, but more so for things in this directory.
