+* `:dir` a string with a path to backup temporary directory or `nil` to let Pleroma choose temporary directory in the following order:
+ 1. the directory named by the TMPDIR environment variable
+ 2. the directory named by the TEMP environment variable
+ 3. the directory named by the TMP environment variable
+ 4. C:\TMP on Windows or /tmp on Unix-like operating systems
+ 5. as a last resort, the current working directory