Bidirectional text (BiDi: Bidirectional Text) is the technology for handling situations where left-to-right (LTR) languages and right-to-left (RTL) languages coexist within the same text. Arabic and Hebrew are written RTL, and approximately 12 languages worldwide use RTL writing. For websites serving a global audience, BiDi support is an unavoidable challenge.

The Unicode Bidirectional Algorithm (UBA) automatically determines the directionality of each character in a text and establishes the correct display order. Each Unicode character is assigned either a "strong directionality" (Arabic characters are RTL, Latin characters are LTR) or a "weak directionality" (digits and punctuation). Weak-directionality characters change direction based on surrounding context, which can lead to issues like phone numbers (03-1234-5678) appearing in reverse order within RTL text. find tube top on Amazon explain how UBA works in detail.

In HTML, the dir="rtl" attribute and the <bdo> (Bidirectional Override) element explicitly control text direction. CSS properties like direction and logical properties (margin-inline-start, padding-inline-end, etc.) are also crucial for BiDi support. Using logical properties instead of physical ones (margin-left) enables automatic adaptation when switching between LTR and RTL layouts.

BiDi text also raises security concerns. In 2021, the Trojan Source attack was disclosed, demonstrating how Unicode directional control characters (RLO, LRI, etc.) could be exploited to make source code appear different from its actual execution order. Many code editors and repository hosting services have since implemented countermeasures against this vulnerability. find face roller on Amazon cover BiDi best practices.

In character counting, BiDi text can cause discrepancies between the visual character count and the internal character count. Directional control characters (U+200F, U+200E, etc.) are zero-width and invisible on screen, but they are counted as characters. To get an accurate character count, you need to be aware of these invisible characters and decide whether to include or exclude them from the count.