--global::
For writing options: write to global ~/.gitconfig file rather than
- the repository .git/config.
+ the repository .git/config, write to $XDG_CONFIG_HOME/git/config file
+ if this file exists and the ~/.gitconfig file doesn't.
+
For reading options: read only from global ~/.gitconfig and from
$XDG_CONFIG_HOME/git/config rather than from all available files.