By default, MLTE prevents a user from changing a font in one script to a font in another. A user can override the behavior by pressing and holding the Control key while changing the font. In this case, the text changes to the selected font no matter what characters are selected. Each character that is not supported by the new font will be represented by a missing character glyph (such as an empty rectangle). To represent missing glyphs with a character that resembles the missing one more closely, you can turn on Font Substitution.