Selection
1.0A selection is, behind the scenes, just a document sized grayscale mask but it's rendered as "marching ants." The ants march along the boundary between less than 50% opaque and more than 50% opaque.
You can:
- Clear the selection with Command-D or Esc
- Invert the selection with Shift+Command+I
- Select all with Command-A
- Store a selection as an alpha channel
- Go into quickmask mode to edit the selection with any painting tools and adjustments you'd use on the main canvas