Unicodebidi

Unicodebidi refers to the Unicode Bidirectional Algorithm (BiDi), a standard method for displaying text that mixes left-to-right and right-to-left scripts. It covers languages such as Arabic and Hebrew in combination with Latin, Cyrillic, and other scripts, within a single line or paragraph. The algorithm assigns each character a directional type (for example L, R, AL, EN, AN, and neutral classes) and an embedding level that governs how text is laid out. It also defines a set of formatting characters, such as LRE, RLE, LRO, RLO, and PDF, used to influence embedding and override behavior, as well as isolate formatting characters like LRI, RLI, FSI, and PDI to create independent directional runs.

The rendering process typically proceeds in stages: resolving explicit embeddings and overrides from the formatting characters, then resolving weak types and neutrals, and finally applying the implicit rules to assign final embedding levels. The characters are then reordered for display according to their embedding levels, producing the correct visual sequence for mixed scripts.

The standard is documented as Unicode Standard Annex No. 9 (UAX 9): The Bidirectional Algorithm. It is implemented in many software components, including web browsers, operating systems, fonts, and text libraries (for example ICU and various language bindings). This makes it essential for multilingual text rendering in editors, terminals, and web content.

Practically, Unicode bidi aims for predictable and reversible rendering across languages. Modern usage often favors isolating sequences to limit spillover effects, and handling emoji and other special cases requires attention to BiDi rules.