TYPO3 uses this directory for temporary files, mainly processed and cached images.
The filenames are cryptic. They are unique representations of the file properties
made by md5-hashing a serialized array with information.
Anyway this directory may contain many thousand files and a lot of them may be of no use anymore.
With this action you can delete the files in this folder. When you do that, you
should also clear the cache database tables afterwards.
This tool will delete files only if the last 10 characters before the extension
(3 chars+'.') are hexadecimal valid ciphers, which are lowercase a-f and 0-9.