whenever working with xdg, you always need to know where to find various files and directories; the authoritative information comes from this spec: XDG Base Directory Specification;

to make it easier to browse this spec, i made a table listing these base directories, their value types, default values and contents:

directory type default content
$XDG_DATA_HOME single $HOME/.local/share user-specific data files
$XDG_CONFIG_HOME single $HOME/.config user-specific configuration files
$XDG_DATA_DIRS ordered set /usr/local/share/:/usr/share/ data files
$XDG_CONFIG_DIRS ordered set /etc/xdg configuration files
$XDG_CACHE_HOME single $HOME/.cache user-specific non-essential (cached) data
$XDG_RUNTIME_DIR single   user-specific runtime files and other file objects