Add

Click between vertices or lines in the same face, and a new line is inserted and the face is divided.

The vertex is inserted by clicking on a line with Shift key.

Original		A line is shown by moving a mouse cursor after clicking a vertex or a line		A new line is inserted and the face is divided by clicking on another vertex or line.

When the [Continuous] option is checked, you can add edges on the neighbor faces continuously. You finish the addition by clicking a right button.

More lines can be added into the neighbor faces by clicking vertices or lines additionally.		Finished by right-button click

Erase

A line shared by two faces is erased and the faces are combined by clicking on the line.

Original		A color of a line is changed when a mouse cursor is over it.		A line is erased by clicking.

Divide

You can put a new vertex on the line when you click on an existing line, and on the cursor position when you drag.

The vertex is created on the middle of the line with Shift key. And it is created on the line only with Ctrl key.

Original		Click on a line, and a new vertex is put.
The position is moved by dragging.		A vertex is insert on the line after releasing a mouse button.

Swap

Click a line shared by two faces, and the line will be swapped clockwise.

Original		A line is shown when the middle edge is clicked		The middle line is swapped