The expansion is performed using text objects, and the text object list used by the plugin can be customised by passing a dictionary to
expand_region#custom_text_objects -- the documentation includes an example of how to do this.
Git Support by Wolfgang Mehner allows Git to be called from within Vim, and it also provides a menu for the commands supported by the plugin. It has some nice features like automatic folds for diffs and logs.
The author has uploaded screenshots on his site that illustrate the main features.