'??? with alpha' format allows you to open images with semitransparency (GIF or PNG) as two parts: image to picture, transparency alpha-channel - to clipboard. In 256-color mode - image will be converted to UNI-palette (Simple or Super according to selected Adaptation in commands menu). You can swap image and alpha-channel for editing of one of them using '0'-'Alpha'-'Picture<->CB'. After you complete editing of image and alpha-channel - you can save both to single PNG file with semitransparency, just select 'Alpha in Clipboard' in PNG saving options.