Gtk.IMContextSimple is a simple input method context supporting table-based
input methods. It has a built-in table of compose sequences that is derived
from the X11 Compose files.
Gtk.IMContextSimple reads additional compose sequences from the first of the
following files that is found: ~/.config/gtk-3.0/Compose, ~/.XCompose,
/usr/share/X11/locale/$locale/Compose (for locales that have a nontrivial
Compose file). The syntax of these files is described in the Compose(5)
Gtk.IMContextSimple also supports numeric entry of Unicode characters
by typing Ctrl-Shift-u, followed by a hexadecimal Unicode codepoint.
For example, Ctrl-Shift-u 1 2 3 Enter yields U+0123 LATIN SMALL LETTER
G WITH CEDILLA, i.e. ģ.