7.39. Add Alpha channel to Selection
creates a selection in the current layer from the Alpha Channel. Opaque
pixels are fully selected, transparent pixels are unselected, and
translucent pixels are partially selected. This selection is
added to the existing selection. The alpha channel
itself is not changed.
The other commands in this group of operations are similar, except that
instead of adding to the existing selection with the selection produced
from the active layer, they either completely replace the selection
with a selection produced from the alpha selection, subtract the alpha
selection from the existing selection, or create a selection that is
the intersection of the two.
7.39.1. Activate the Command
Applying “Add to Selection”