Each tool has several modes, which can be found in the tool bar.
These modes allow a tool to draw or modify objects in different ways.
The different modes of a tool are always divided into sections, according to the function of the mode groups, separated by a |
The shortcut keys U, I,O,P,^ and $, allow you to change the active method within the group to make your editing faster.
Each group has its own hot key, always starting with The U. Pressing the shortcut key repeatedly changes the mode in the group or opens a dialog box with the tool settings.
Not every tool has six mode groups. For example, some tools may only apply to U and I.