The Unicode Bidirectional Text Algorithm

The Unicode® Bidirectional Algorithm (also known as the BiDi Algorithm) is part of the Unicode text standard that describes how the user agent should order characters while rendering Unicode text. Understanding this algorithm in at least basic terms is helpful when you're striving to produce localization-ready web content or apps.

In this guide, we'll take a look at the BiDi Algorithm and learn in general what it does and how it applies to your content, so that you'll be better prepared when using the features of HTML and CSS to which the algorithm applies while determining the order and directionality of text during rendering.

Fundamentals

(base direction, character types, etc)

The algorithm

Character level directionality

Directional runs

(what they are, how base direction applies)

Handling neutral characters

Overriding the algorithm

Content about using HTML and CSS to override the default behavior of the algorithm; include info about isolating ranges etc.

Overiding BiDi using Unicode control characters

Unicode provides a number of special control characters that make it possible to control directionality of ranges of text. There are two sets of control characters; one set opens the override, and another restores the original directionality. You must always follow each opening character with an appropriate closing character.

See also

• Unicode® Standard Annex #9: Unicode Bidirectional Algorithm
• W3C: Unicode Bidirectional Algorithm basics
• W3C Q&A: How to use Unicode controls for bidi text