[Plugin: Members] What exactly do the capabilities do?

The documentation is reasonably clear on how this plugin works except for one, critical piece of information: What do the various capabilities control?

Some are obvious, like activate_plugins and edit_others_posts. But others are mysterious: What exactly does modify_options control?

I want to give some of my users access to plugin settings pages, so they can adjust the settings in other plugins. Where is that control?

http://ww.wp.xz.cn/extend/plugins/members/