What is خوارزمية ثنائية الاتجاه?

خوارزمية تحدد ترتيب عرض الأحرف في النص متعدد الاتجاهات (مثلاً إنجليزي + عربي)، باستخدام فئات bidi للأحرف والتجاوزات الاتجاهية الصريحة.

What is فئة ثنائية الاتجاه?

خاصية تحدد كيفية تصرف الحرف في النص ثنائي الاتجاه (LTR, RTL، ضعيف، محايد)؛ تُستخدم بواسطة Unicode Bidirectional Algorithm لتحديد ترتيب العرض.

الطباعة الفنية

RTL (Right-to-Left)

اتجاه النص حيث تتدفق الأحرف من اليمين إلى اليسار. تستخدمه العربية والعبرية والتانا والكتابات الأخرى؛ يتطلب Bidirectional Algorithm للعرض الصحيح.

2023-06-12 · Updated 2024-08-21

What is RTL (Right-to-Left)?

RTL stands for Right-to-Left, describing text that is written and read from right to left. Arabic, Hebrew, Persian (Farsi), Urdu, and several other scripts are inherently RTL. This is not a stylistic choice — it is the fundamental direction of these writing systems, as fixed by their orthographic traditions dating back thousands of years. Proper RTL support requires changes at every layer of text technology: from Unicode's bidirectional algorithm to CSS properties to HTML markup.

Unicode Bidirectional Algorithm (Bidi)

The Unicode Bidirectional Algorithm (UAX #9) is the specification for how to display text that mixes LTR and RTL content — called bidirectional or bidi text. Because a single paragraph might contain English, Arabic, and numbers all together, a strict mechanical rule set is needed to determine the display order of each run.

The algorithm assigns every character a bidi category: - L (Left-to-Right): A–Z, Latin digits, most punctuation - R (Right-to-Left): Hebrew characters - AL (Arabic Letter): Arabic, Thaana, Syriac characters - AN (Arabic Number): Arabic-Indic digits - EN (European Number): 0–9 ASCII digits

The algorithm then resolves the visual ordering based on the paragraph's base direction and these per-character categories.

Bidi Control Characters

Unicode provides invisible characters to explicitly override the automatic bidi behavior:

Character	Unicode	Name	Effect
RLM	U+200F	Right-to-Left Mark	Forces bidi context rightward
LRM	U+200E	Left-to-Right Mark	Forces bidi context leftward
RLE	U+202B	Right-to-Left Embedding	Start RTL embedding
LRE	U+202A	Left-to-Right Embedding	Start LTR embedding
RLO	U+202E	Right-to-Left Override	Force all text RTL
LRO	U+202D	Left-to-Right Override	Force all text LTR
PDF	U+202C	Pop Directional Formatting	End an embedding/override
RLI	U+2067	Right-to-Left Isolate	RTL bidi isolate (modern)
LRI	U+2066	Left-to-Right Isolate	LTR bidi isolate (modern)
PDI	U+2069	Pop Directional Isolate	End isolate

The RLO character (U+202E) was notoriously abused in filenames to disguise file extensions: Vacation‮gpj.exe would display as Vacationgpj.exe visually.

RTL in HTML and CSS

<!-- Set paragraph direction -->
<p dir="rtl">مرحبا بالعالم</p>

<!-- HTML attribute on document root -->
<html lang="ar" dir="rtl">

<!-- Use the <bdi> element for user-generated content of unknown direction -->
<p>Posted by <bdi>محمد</bdi> yesterday</p>

/* CSS direction property */
.arabic-text {
  direction: rtl;
  text-align: right; /* or use text-align: start (logical) */
}

/* CSS logical properties (preferred for bidi) */
.box {
  margin-inline-start: 1em;  /* left in LTR, right in RTL */
  padding-inline-end: 0.5em; /* right in LTR, left in RTL */
  border-inline-start: 2px solid; /* left border in LTR */
}

Mirroring in RTL

When a UI is mirrored for RTL, directional icons must also be mirrored: a "forward" arrow in LTR points right (→), but in RTL it should point left (←). Layout elements like sidebars, toolbars, and scrollbars typically mirror position.

Quick Facts

Property	Value
RTL scripts	Arabic, Hebrew, Persian, Urdu, Thaana, Syriac, N'Ko, Tifinagh
Unicode bidi spec	UAX #9 (Unicode Standard Annex 9)
HTML direction attribute	`dir="rtl"` or `dir="ltr"`
CSS property	`direction: rtl`
Right-to-Left Mark	U+200F (RLM)
Right-to-Left Override	U+202E (RLO) — security risk
Modern isolate characters	RLI (U+2067), LRI (U+2066), PDI (U+2069)
CSS logical properties	`margin-inline-start`, `padding-inline-end` for bidi-aware layout

المصطلحات ذات الصلة

خوارزمية ثنائية الاتجاه فئة ثنائية الاتجاه