1) For each key binding, you can bound multiple keys, and in order to activate this function, you need to press all bound keys. Example: ctrl + M
2) For one button you can bind unlimited amount of actions, and all of them will work... For example, you can bind "strafe left" and "go forward" to W, and when you will press W, you will go diagonally forward-left
3) You can mix and match those. Example: you can bind "wrench mode" to M and "jetpack mode" to ctrl + M, then if you will press M, wrench mode will be switched, and if you press ctrl + M, jetpack and wrench mode will be switched...
4) If you wish, you can configure to detect key presses while gui is opened. Allows walking while looking in your inventory for example!