The meaning of the first three optional parameters is exactly the same as in the Allow command.
It is possible to use multiple pattens in the same CheckOnly commands.
When processing documents with URL
pattern, indexer uses
the HTTP HEAD method
(instead of the usual HTTP GET).
It means that the document is checked only for existence, while
the document content is not downloaded.
CheckOnly can be useful for a FTP search engine (searching through file names rather than file contents), for *.zip, *.exe, *.arj and other binary files, as well as in case of using indexer for link validation.
CheckOnly takes global effect for the entire configuration file and can be used multiple times.