Ligatures

Figure 1: The Tamil keyboard in the shifted state, showing linguistic characters Sri and Ksa as Ligatures

Figure 2: A keyboard layout for Deseret, a language using supplementary characters (each represented by "Ligatures" of UTF-16 of high and log surrogates)

Figure 3: A very silly (but real!) keyboard layout (created by a developer for personal use). This shows the 4 UTF-16 character limit for a single keystroke.