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diff --git a/termbox2/egc.ha b/termbox2/egc.ha
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+// If set, enable extended grapheme cluster support (see
+// [[termbox2::extend_cell]] and [[termbox2::set_cell_ex]]). Consumes more
+// memory. Defaults on.
+export def OPT_EGC: bool = true;
+
+// A cell in a 2d grid representing the terminal screen.
+//
+// The terminal screen is represented as a 2d array of cells. The structure is
+// optimized for dealing with single-width (wcwidth==1) Unicode codepoints,
+// however some support for grapheme clusters (e.g., combining diacritical
+// marks) and wide codepoints (e.g., Hiragana) is provided through ech via
+// [[termbox2::set_cell_ex]]. ech is only valid if it is non-empty, otherwise
+// ch is used.
+//
+// For non-single-width codepoints, given W=wcwidth(ch || ech):
+//
+// - when W<=0: termbox forces a single-width cell. Callers should avoid this
+//   if aiming to render text accurately. Callers may use
+//   [[termbox2::set_cell_ex]] or [[termbox2::print]] or similar to render
+//   W==0 combining characters.
+// - when W>=2: termbox zeroes out the following W-1 cells and skips
+//   sending them to the tty. So, e.g., if the caller sets x=0,y=0 to a
+//   W==2 codepoint, the caller's next set should be at x=2,y=0. Anything
+//   set at x=1,y=0 will be ignored. If there are not enough columns
+//   remaining on th eline to render W cells, spaces are sent instead.
+export type cell = struct {
+        ch: u32, // a Unicode codepoint
+        fg: uattr, // bitwise foreground attributes
+        bg: uattr, // bitwise background attributes
+        ech: []rune, // a grapheme cluster of Unicode codepoints
+};