There is an interesting irony here.<p>This library is layered on top of a package called CrossTerm, which (on terminal systems, at least, but not on console systems) in turn emits roughly ECMA48 standard control sequences to do the cursor motions and whatnot. So the bottom layer is a terminal/terminal emulator that supports/emulates a (subset of a) DEC VT520 terminal.<p>But VT520s <i>can already do what the library does</i>. This idea of a static region and a scrolling region on the screen has, after all, been around in the world of terminals since the 1970s. There are DEC VT control sequences for setting left, right, top, and bottom margins; which specify a scrolling region and also modify scrolling and automatic cursor movement behaviours outwith that region. They're widely supported in terminal emulators because a popular compatibility testing program, vttest, makes them applicable to many tests.<p>So what is actually going on here is that because CrossTerm does not produce anywhere near the full capabilities of an underlying DEC VT, an entire library has been built on top of it to replicate stuff that actually exists already in the code of the terminal emulators and terminal firmwares. It should be noted that the termcap and terminfo libraries provide a change_scroll_region capability that can set top and bottom margins, and are superior to CrossTerm in that regard.<p>The curious should see the DECSTBM and DECSLRM control sequences and the DECLRMM private mode.