keywords (modifiers and literals)

modifiers (\):
```
fn

cmd
lcmd
rcmd

shift
lshift
rshift

alt
lalt
ralt

ctrl
lctrl
rctrl

hyper (cmd + shift + alt + ctrl)

meh (shift + alt + ctrl)
```

key literals:
```
"return" (kVK_Return)
"tab" (kVK_Tab)
"space" (kVK_Space)
"backspace" (kVK_Delete)
"escape" (kVK_Escape)

The following keys can not be used with the fn-modifier:

"delete" (kVK_ForwardDelete)
"home" (kVK_Home)
"end" (kVK_End)
"pageup" (kVK_PageUp)
"pagedown" (kVK_PageDown)
"insert" (kVK_Help)
"left" (kVK_LeftArrow)
"right" (kVK_RightArrow)
"up" (kVK_UpArrow)
"down" (kVK_DownArrow)
"f1" (kVK_F1)
"f2" (kVK_F2)
"f3" (kVK_F3)
"f4" (kVK_F4)
"f5" (kVK_F5)
"f6" (kVK_F6)
"f7" (kVK_F7)
"f8" (kVK_F8)
"f9" (kVK_F9)
"f10" (kVK_F10)
"f11" (kVK_F11)
"f12" (kVK_F12)
"f13" (kVK_F13)
"f14" (kVK_F14)
"f15" (kVK_F15)
"f16" (kVK_F16)
"f17" (kVK_F17)
"f18" (kVK_F18)
"f19" (kVK_F19)
"f20" (kVK_F20)

"sound_up" (NX_KEYTYPE_SOUND_UP)
"sound_down" (NX_KEYTYPE_SOUND_DOWN)
"mute" (NX_KEYTYPE_MUTE)
"play" (NX_KEYTYPE_PLAY)
"previous" (NX_KEYTYPE_PREVIOUS)
"next" (NX_KEYTYPE_NEXT)
"rewind" (NX_KEYTYPE_REWIND)
"fast" (NX_KEYTYPE_FAST)
"brightness_up" (NX_KEYTYPE_BRIGHTNESS_UP)
"brightness_down" (NX_KEYTYPE_BRIGHTNESS_DOWN)
"illumination_up" (NX_KEYTYPE_ILLUMINATION_UP)
"illumination_down" (NX_KEYTYPE_ILLUMINATION_DOWN)
```

keycodes:

OR

Launch **skhd** in observer mode: `skhd --observe` or `skhd -o`. Press `ctrl+c` to quit.

Start with skhd --observe (or -o) to inspect the key names and keycodes listed in the issue, then trace where modifier and literal keywords are parsed. Compare the macOS key constants shown in the issue with the accepted syntax. Done means the listed modifiers and literals are consistently recognized, including the documented fn limitations.

Written by the indexing model from the issue text.