/var/tmp should have permissions
rwxrwxrwt, which allow anyone to change to this directory, create and read files in this directory and write/rename/delete files they own (this last restriction is caused by the
t in the permissions, which is the "sticky bit").
The file you see in there is a temporary file created by something on your system. You can look at its ownership or try and see what process has it open to get a clue as to what wrote it. The XML schema in the top of the file may also help out with that.
The folder above
/, also know as the