This ZMK firmware configuration was forked from urob's zmk-config and consists of a 42-keys layout designed for the Corne. It uses the Colemak keyboard layout, but can be toggled to a modified QWERTY layout for playing games with WASD movement. It is my daily driver for general typing, programming, navigation, and gaming.

The description below is a slight variation of urob's README, edited for my own personal use. Any use of first-person language is from urob's perspective and not my original work.

⌨️ Keymap Image Status: Up to date!

• "Timeless" homerow mods
• Combos replace symbol layer
• Smart numbers and mouse layers auto-toggle off
• Leader key template ready to be customized zmk-helpers
• Arrow-cluster doubles as home, end, begin/end of document on long-press
• More intuitive shift-actions: , ;, . : and ? !
• Gaming layer toggle that switches to a shifted QWERTY layout

• Noticeable delay when tapping HRMs: Increase require-prior-idle-ms. As a rule of thumb, you want to set it to at least 10500/x where x is your (relaxed) WPM for English prose.¹
• False negatives (same-hand): Reduce tapping-term-ms (or disable hold-trigger-key-positions)
• False negatives (cross-hand): Reduce require-prior-idle-ms (or set flavor to hold-preferred -- to continue using hold-trigger-on-release, you must also patch ZMK or use an already patched branch)
• False positives (same-hand): Increase tapping-term-ms
• False positives (cross-hand): Increase require-prior-idle-ms (or set flavor to tap-preferred, which requires holding HRMs past tapping term to activate)

• The top vertical-combo row matches the symbols on a standard numbers row (except + and & being swapped)
• The bottom vertical-combo row is symmetric to the top row (subscript _ aligns with superscript ^; minus - aligns with +; division / aligns with multiplication *; logical-or | aligns with logical-and &)
• Parenthesis, braces, brackets are set up symmetrically as horizontal combos with <, >, { and } being accessed from the Navigation layer (or when combined with Shift)
• Left-hand side combos for tap, esc, enter, cut (on X + D), copy and paste that go well with right-handed mouse usage
• W + P activates the smart mouse layer

Inspired by Jonas Hietala's Numword for QMK, I implemented my own Auto-layer behavior for ZMK to set up Numword. It is triggered via a single tap on "Smart-Num". Numword continues to be activated as long as I type numbers, and deactivates automatically on any other keypress (holding it activates a non-sticky num layer).

After using Numword for more than a year now, I have been overall very happy with it. When typing single digits, it effectively is a sticky-layer but with the added advantage that I can also use it to type multiple digits.

The main downside is that if a sequence of numbers is immediately followed by any of the letters on which my numpad is located (WFPRSTXCD), then the automatic deactivation won't work. But this is rare -- most number sequences are terminated by space, return or some form of punctuation/delimination. To deal with the rare cases where they aren't, there is a CANCEL key that deactivates Numword, Capsword and Smart-mouse. (It also toggles off when pressing Numword again, but I find it cognitively easier to have a dedicated "off-switch" than keeping track of which modes are currently active.)

Similarly to Numword, I have a smart-mouse layer (activated by comboing F + P), which adds scroll and mouse-movements, and replaces the right thumbs with mouse buttons. Pressing any other key automatically deactivates the layer.

My left thumb triggers three variations of shift: Tapping after any alpha key yields key-repeat (to reduce SFUs). Tapping after any other keycode yields sticky-shift (used to capitalize alphas). Holding activates a regular shift, and double-tapping (or equivalently shift + tap) activates ZMK's Caps-word behavior.

One minor technical detail: While it would be possible to implement the double-tap functionality as a tap-dance, this would add a delay when using single taps. To avoid the delays, I instead implemented the double-tap functionality as a mod-morph.

To economize on keys, I am using hold-taps on my navigation cluster, which yield home, end, begin/end of document, and delete word forward/backward on long-presses. The exact implementation is tweaked so that Ctrl is silently absorbed in combination with home and end to avoid accidental document-wide operations (which are accessible via the dedicated begin/end document keys.)

I am using Nick Conway's fantastic tri-state behavior for a one-handed Alt-Tab switcher (PWin and NWin).

I recently started using Nick Conway's Leader key implementation for ZMK. From my limited experience, I really like how it allows making less commonly used behaviors accessible without binding them to a dedicated key. For now I am using it for a variety of Unicode math symbols and international characters. I am planning to extend the use to various firmware interactions once I figure out the technical details.

NOTE: See zmk-helpers for instructions on how to set up unicode and international characters for the leader key. As of right now, the leader key has no sequences implemented.

Since I switched from QMK to ZMK I have been very impressed with how easy it is to set up relatively complex layouts in ZMK. For the most parts I don't miss any functionality (to the contrary, I found that ZMK supports many features natively that would require complex user-space implementations in QMK). Below are a few remaining issues:

• ZMK does not yet support "tap-only" combos (#544), requiring a brief pause when wanting to chord HRMs that overlap with combo positions. As a workaround, I implemented all homerow combos as homerow-mod-combos. This is good enough for day-to-day, but does not address all edge cases (eg changing active mods).
• Very minor: &bootloader doesn't work with stm32 boards like the Planck (#1086)