PhotoPlus X6 User Guide - Serif

Storing selections
Manipulating Images 87
You can store selections (i.e., just the marqueed region and per-pixel
selectedness data) as part of either the current image or any open image file, and
load a stored selection at any time. It's often useful to be able to "grab" the same
region of an image at different phases of working on it. And, for repetitive tasks
(preparing web buttons, for example) on different but graphically similar files,
by storing a selection you can reuse it rather than having to recreate it for each
file.
Selections are created and stored exclusively as alpha channels in the Channels
tab; Once stored, they can be retrieved from the tab at any time.
As each alpha channel behaves like a mask (p. 27) you can paint on the alpha
channel at different greyscale levels for different levels of "selectedness". The
White or light portions of the mask reveal layer pixels (make them more
opaque). Black or dark portions hide layer pixels (making them more
transparent).