1.3.2 Symmetrical Swapping

Some characters have a meaning related to their direction, such as greater than (>) and less than (<). Bidirectional text strings containing these characters may need to replace one character with its complement to retain the correct meaning. For example, the expression 3 < 4 (three is less than four) is stored in the sequence in which it is typed. To display this expression correctly in a right-to-left string, however, it must appear as 4 > 3 (read right to left as 3 less than 4). Because a direct transposition of the three characters in storage would give 4 < 3, which is incorrect, the transformation process must swap < and >.

Replacing complementary symbols to retain their correct meaning is called symmetrical swapping. Characters requiring symmetrical swapping include parentheses: ( and ), angle brackets: < and >, square brackets: [ and ], and curly brackets: { and }.