Select Rectangle Area Tool

• apply effects to it
• change its transparency level
• copy to the clipboard 
• draw in this area only (operation of all drawing tools to be distributed to selected area only)
• move and resize the selected object

If the image hasn't been selected then double-clicking on the Select rectangle area button selects the entire image. If any area of the image has been selected already then double clicking will cancel the selection. It is possible to deselect by clicking the right mouse button on the edit area or clicking the mouse on a non-selected area.

If the transparent mode modifier is enabled, transparent pixels won't be drawn.