I don't know whether this is a flaw or intentional in Photoshop CC 2019 (and possibly earlier versions), but Save for Web changes the resolution of the resulting jpg or png image to 72 dpi (or ppi), regardless of the actual resolution of the originating file. Discovered this while preparing a jpg banner (advertisement) for a publisher that required a 782x90 pixel jpg at 300 dpi (reason for that resolution is unknown). Had to use Save As... to avoid the change in resolution to 72 dpi. It's bad enough that the user is not allowed to set resolution in Save for Web (despite its undeserved "legacy" status), but I can't find any documentation of this in the Save for Web window or online. This is very user unfriendly. I'm posting it because even though Adobe is almost certain to ignore it, other users may benefit from knowing about it.