The Unicode characters are associated with several properties that specify how various processes related to text rendering (i.e., drawing text on the screen or on paper) should handle them.
The Unicode standard includes a very detailed specification of how characters from right-to-left and left-to-right writing systems are to be arranged when intermixed in a single line of text. Central to this specification are the characters' bi-di categories, which are given in the UnicodeData.txt file using these codes:
|L||Strong left-to-right characters.|
|R or AL||Strong right-to-left characters.|
|EN and AN||Digits, which have weak left-to-right directionality.|
|ES, ET, and CS||Punctuation marks used with numbers. Treated ...|