How to Define Your Own Gmail Keyboard Shortcuts

The manual is clear about it: "CTRL/K causes the cursor to move non-destructively to the same character position in the line immediately above the current line."
Not into manuals? No problem.
ADM-3A, one of the 1970s' first widespread terminals for computers, came with "a keyboard that resembles the keyboard of a conventional typewriter". Above the H, J, K and L keys hovered additional symbols: ←↓↑→.
Bill Joy developed the text editor vi on an ADM-3A, dropped the CTRLkey and used HJKL to navigate text. That's why Gmail today uses J and K to navigate messages.
Whether you'd like to drop that legacy or add more ADM-3A mappings(- is RUB, for example), you can:
›› Want to command Gmail with your keyboard, and rule it fully? Here's how to set up your own Gmail keyboard shortcuts.