Fossil uses the file _FOSSIL_ on Windows but on all other operating systems it prefers .fslckout (either will work but those are the names used by the software when you create checkouts).
You can see this documented in the Fossil Glossary in the "Checkout" section where it says:
Check-out directories are associated with the repos they were created from by settings stored in the check-out directory. This is in the .fslckout file on POSIX type systems, but for historical compatibility reasons, it’s called FOSSIL by native Windows builds of Fossil.
Basically the use of _FOSSIL_ on Windows is for historical windows file systems that don't support more than three characters as an extension.
Fossil uses the file
_FOSSIL_
on Windows but on all other operating systems it prefers.fslckout
(either will work but those are the names used by the software when you create checkouts).You can see this documented in the Fossil Glossary in the "Checkout" section where it says:
Basically the use of
_FOSSIL_
on Windows is for historical windows file systems that don't support more than three characters as an extension.