Problem of Dual-Purpose Keys (home row mods)

What is Dual-Purpose Key

Some keyboard software have a feature to assign a modifier key and a non-modifier key both to the same physical key. For example, set Control and Space both to the Space key. When you press and release Space, it inserts a space, but when you press and hold Space, then press for example c, it does Ctrl+c (copy).

Software that Support Dual-Purpose Key

• UHK Agent for Ultimate Hacking Keyboard
• QMK [see QMK Configurator Tutorial]
• XCAPE for Linux X11 [see Linux: Keyboard Software Guide]
• Karabiner-Elements for Mac [see Mac Keyboard Software Guide]

What is Home Row Mods

Home Row Mods is setting your home row keys to become modifiers. For example

Problem of Home Row Mods

One problem of Home Row Mods is random accidental invocation of key shortcuts, if you are a fast typer.

Problem of Dual-Purpose Keys

When you have a dual-purpose key, you cannot hold the key to repeat.

I know because i used Dual-Purpose Keys on my Gergo Keyboard (QMK firmware), also with on my Ultimate Hacking Keyboard (UHK Agent firmware) .

• 
  Gergo keyboard

• 
  Ultimate Hacking Keyboard

Try this. Whip your keyboard out. Program the Backspace ⌫ key to be also Ctrl when held down. Now, see if you can hold Backspace ⌫ to delete letters continuously. You can't.

QMK Solution of Dual-Purpose Key Hold to Repeat

2021-04-23 Hans Peter wrote to say that in QMK, the dual-purpose key problem of hold to repeat can be avoided, by press and release the key, then hold it, then the non-modifier function of the key would repeat.

Hold to Repeat is Also a Hack

Keyboard Technology, It's Hack All the Way