The button in the Toolbox let us switch between "Quick Mask" and "Standard" editing modes.
Click
button* to enter Quick Mask mode.
Edit mask using any painting, filling, and selecting tools.
Click
button* to enter Standard Editing mode.
* In Photoshop CS3, you turn "Quick Mask" on/off with the same button. ** Selections and quick masks are discussed in the 2nd chapter of this video-course
button in the Toolbox let us switch between "Quick Mask" and "Standard" editing modes.
button