One of the MIDI filter actions that I use most often, namely
Deselect all events outside time selection (aka Limit selection of MIDI events to time selection), is not available in REAPER.
When a user selects pitches by left-clicking or -dragging on the piano keys in the piano roll, the user often does not intend to edit ALL notes of the selected pitches over the entire item. Similarly, when the a user selects events at certain positions in measures using the Filter Events dialog box, it is obviously useful to be able to limit selection to time selection.
I therefore suggest that this function be included as a built-in action (that can be linked to a menu button), as well as a clickable option in the Filter Events dialog box.
A demo script is given in the thread
Simple but useful MIDI editor tools: warp, stretch, deselect etc