On Mac OS X, these shortcuts Ctrl + B, Ctrl + K belong to Mac's readline shortcut: https://jblevins.org/log/kbd
Since Stack Overflow's editor has used Cmd + B/K as a shortcut for editing, there isn't any need to take up the shortcut keys of the Mac system.
I recommend the following shortcuts for Mac OS X users.
- Ctrl + B Move Cursor Backwards
- Cmd + B Bold Text
- Ctrl + K Delete Text Forwards Line
- Cmd + K Code Sample