Refers to the script’s ability to handle text that reads both left to right and right to left. For example, in the bidirectional rendering of Arabic, the default reading direction for text is right-to-left, but for numbers, it is left-to-right. Processing a complex script must account for the difference between the logical (keystroke) order of input and the visual order of the output glyphs. In addition, processing must properly deal with caret movement and hit testing. The mapping between screen position and a character index for, say, selection of text or caret display requires knowledge of the layout algorithms.