v0.1.92
Documentation, checked rather than assumed: exactly what the Android 4 build does with the notepad and with direct code-point entry — which is all of it, spelled out feature by feature. Undo there is the notepad's own history (TextView's is API 23), and the clipboard goes through setPrimaryClip, which has been there since API 11.
Two things do differ, and both are now named: the floating panel's bar spells its glyphs as words below API 21, and a character your device has no glyph for shows as a box while still being the character that was typed.
Verified by drawing the real views with the legacy APK on an Android 4.4.2 image; those two pictures are in the README.
Reproducibility re-verified at this tag under JDK 21.