Extracting AppImages

All recent type 2 AppImages (created with an appimagetool newer than Nov 15, commit #51fdac2) can be run with extra parameters, all with a naming pattern "*--appimage-<something>". You can list them all by running it with --appimage-help:

./WhatEver-x86_64.AppImage --appimage-help
AppImage options:

--appimage-extract              Extract content from embedded filesystem image
--appimage-help                 Print this help
--appimage-mount                Mount embedded filesystem image and
                                print mount point, then wait for kill with Ctrl-C
--appimage-offset               Print byte offset to start of
                                embedded filesystem image
--appimage-signature            Print digital signature embedded in AppImage
--appimage-updateinfo[rmation]  Print update info embedded in AppImage
--appimage-version              Print version of AppImageKit

If you run ./WhatEver-x86_64.AppImage --appimage-extract, the AppImage will auto-extract its contents into AppDir (currently as a sub-directory squashfs-root in the current location. Then just change into that directory to look around and see what elements the AppImage is composed from.