Fails, succeeds, or partial read due to EOF (returns num read) return value: -1: unrecoverable error <n>: number of bytes read

Override */

traverse the layout to locate the nearest character to a display position

API click: on mouse down, move the cursor to the clicked location, and reset the selection

discard the oldest entry in the undo list

API drag: on mouse drag, move the cursor and selection endpoint to the clicked location

find the x/y location of a character, and remember info about the previous row in case we get a move-up event (for page up, we'll have to rescan)

stb_textedit internally allows for a single undo record to do addition and deletion, but somehow, calling the stb_textedit_paste() function creates tw

canoncialize the selection so start <= end

find minimum y position if it starts at x1

rects array must be big enough to accommodate all characters in the given ranges

check if a utf8 string contains a prefix which is the utf16 string; if so return length of matching utf8 string