Using "keyboard shortcuts on Android" phone without a physical keyboard:

Chrome browser + github
Install Hacker’s Keyboard

In Settings enable Use permanent notification
Normally a keyboard only activates in an input area, but now one can just click the permanent “Show Hacker’s Keyboard” notification - and use all the useful shortcuts “to” “tr” “tt” “ctr+up” “ctrl+z” etc.

In Settings you can also enable “Gesture and Key actions” to use left/right swipe OR volume up/down to change keyboard size quickly.