update TODO

TODO.md

@@ -18,6 +18,11 @@ Correctness:
 * `exit` in the shell should close the window
 * test wrap against wraptest: https://github.com/mattiase/wraptest
   - automate this in some way
+* Charsets: UTF-8 vs. ASCII mode
+  - we only support UTF-8 input right now
+  - need fallback glyphs if they're not supported
+  - can effect a crash using `vttest` menu `3 10` since it tries to parse
+    ASCII as UTF-8.
 
 Improvements:
 
@@ -37,4 +42,3 @@ Major Features:
 * Sixels: https://saitoha.github.io/libsixel/
 * Kitty keyboard protocol: https://sw.kovidgoyal.net/kitty/keyboard-protocol/
 * Kitty graphics protocol: https://sw.kovidgoyal.net/kitty/graphics-protocol/
-* Charsets (i.e. line drawing, `CSI ( B` and so on)