A_HotkeyModifierTimeout is a built-in variable that affects the behavior of Send with hotkey modifiers Ctrl, Alt, Win, and Shift. Specifically, it defines how long after a hotkey is pressed that its modifier keys are assumed to still be held down. This is used by Send to determine whether to push the modifier keys back down after having temporarily released them.
A_HotkeyModifierTimeout can be used to get or set an integer representing the length of the interval in milliseconds. If -1, it never times out (modifier keys are always pushed back down after the Send). If 0, it always times out (modifier keys are never pushed back down).
The default setting is 50 (ms).
This variable has no effect when:
To illustrate the effect of this variable, consider this example: ^!a::Send "abc".
When the Send function executes, the first thing it does is release Ctrl and Alt so that the characters get sent properly. After sending all the keys, the function doesn't know whether it can safely push back down Ctrl and Alt (to match whether the user is still holding them down). But if less than the specified number of milliseconds have elapsed, it will assume that the user hasn't had a chance to release the keys yet and it will thus push them back down to match their physical state. Otherwise, the modifier keys will not be pushed back down and the user will have to release and press them again to get them to modify the same or another key.
The timeout should be set to a value less than the amount of time that the user typically holds down a hotkey's modifiers before releasing them. Otherwise, the modifiers may be restored to the down position (get stuck down) even when the user isn't physically holding them down.
You can reduce or eliminate the need for this variable with one of the following: