The meaning of the first three optional parameters is exactly the same
as in Allow command.
Indexer will use HEAD instead of GET HTTP method for URLs that
matches/doesn't match given argument. It means that the file
will be checked only for existence and will not be downloaded.
Useful for zip, exe, arj and other binary files.
Note that you can disallow those files with commands given below.
You may use several arguments for one "CheckOnly" commands.
More useful, for example, for searching through the URL names rather than
for the contents (a la FTP-search).
Takes global effect for configuration file.