Standard Arabic—a.k.a. Modern Standard Arabic or Literary Arabic—is the standardized and literary variety of Arabic used in writing and in most formal speech in countries of Northern Africa and West Asia. Regional and classical dialects of Arabic may differ in layout and text details and arenot covered by this document.

However, there are some major differences in common practices between theWestern Arab regions—that is North-West Africa—andEastern Arab regions—which is North-East Africa and West Asia. For example, the numeral digits used in the two regions and their formatting are vastly different. Although, there's no clear line between the Eastern and Western Arab regions.

Persian—a.k.a. Modern Persian—is the standardized and literary variety of the official languages used in Iran and Afghanistan. The dialect of Persian in Iran is also called Western Persian, and is locally known asFarsi. The dialect of Persian in Afghanistan is also known as Eastern Persian, and is locally known as Dari.

Tajik—a.k.a Tajiki or Tajiki Persian—is the Persian language as used in Tajikistan. It is written in the Cyrillic script, therefore, isnot covered by this document.

In situations where short runs of text run vertically, for example on book spines or in table headers, Arabic text is rotated to run along the line. It may be rotated so that the tops of the letters face to the left (read the text from top to bottom) or to the right (read the text from bottom to top).

 

The flow of text, top-down vs. bottom-up, may depend on regions or authors. The leftcase inFigure1 is a typically francophone style for bookspines, whereas the right case is an anglophone style.

2.1.1.1Arabic embedded in vertically orientated text

When Arabic is embedded in body text that is set vertically, such as CJK or Mongolian text, it is also normally rotated so as to run along the line. Typically, the Arabic text will be read from bottom to top of the line.

When the Arabic text spans more than one line, the text is wrapped in the same way as it would be in horizontal text, ie. the first part of the Arabic text is kept on thefirst line, and subsequent parts of the Arabic text appear on subsequent lines.Therefore, in the case of Mongolian, where lines are read left-to-right, the Arabic text lines are also read left-to-right, whereas in Chinese or Japanese, where vertical lines are normally read right-to-left, the Arabic text lines are also read right-to-left.

2.1.1.2Upright vertical Arabic text

There are attested cases of Arabic text arranged vertically with the letters upright, for example in signboards for cinemas or theatres. It is not clear, at this point whether this a standard approach for Arabic text, or just an unusual layout that mimics Western typographic approaches.

The following should be noted inFigure3.

1. Letters flow from top to bottom (as with Latin script).
2. Isolated form of letters seems more appropriate here than the joined form.
3. Diacritic marks, if any, must be applied to letters and not appear on separatelines.

TheUnicode Bidirectional Algorithm (orbidi algorithm, for short) [UAX9] details an algorithm for rendering right-to-left text and covers a myriad of situations, mixing different kinds of characters. A simpler explanation of the basics of the algorithm exists in theW3C articleUnicode Bidirectional Algorithm basics. [UBA-BASICS] You can refer to these documents for more information about Unicode’s bidirectional algorithm.

A brief overview of thebidirectional algorithm follows, because the direction is an essential part of how Arabic script is used.

The characters of a text are digitally stored and transferred in the same order that they are typed by a user. This is the order in which the text is read and pronounced by people and held in memory by software applications, as shown inFigure4 for a sample text.

But the order used when displaying text is different. The purpose of the bidi algorithm is to find display positions for the characters of a text. These positions are solely used for displaying texts.Figure5 shows the same sample text when prepared for display with the bidi algorithm.

An initial step of the process involves determining each paragraph’sbase direction: whether the paragraph is left-to-right or right-to-left. The base direction is either explicitly set by the author, inherited from the page, or (typically for user-generated content) detected based on the content of the paragraph. The base direction has two important uses later in the process.

The next step is to split the text intodirectional runs. Each directional run is a sequence of characters with the same direction.

Inside each run, all the characters follow the same order. The runs themselves are ordered for visual representation from left to right or from right to left, depending on the base direction of the paragraph.Figure7 demonstrates an example of this. This is the first effect of the base direction.

Unicode has abidi class (orbiditype) property defined for each character that is used to determine the direction of each character. All the Arabic letters are marked as right-to-left characters, while Latin characters have the left-to-right category.

Some characters, mostly punctuation marks, areneutral. Thedirection of these characters is derived from their surrounding characters. If a neutral character is surrounded by characters of the same direction (e.g. a space surrounded by Arabic letters), it gets the direction of its neighbors. Otherwise (e.g. a space between an Arabic and a Latin, or a neutral character appearing at the start or the end of a paragraph), the neutral character gets its direction from the paragraph’s base direction. This is another effect of the base direction in the bidi algorithm.

The above explanation of the bidi algorithm is highly simplified, to convey only theessentials of how Arabic text is transformed for rendering. The actual algorithm deals with many more character types and edge cases. Please refer toUnicodeBidirectional Algorithm basics [UBA-BASICS] for more information orUnicode Bidirectional Algorithm [UAX9] for the official detailed documentation.

Letters may join through a finely inclined line.

Or they may appear on two, square-ended lines.

Multilevel baselines don't occur in all fonts. The above examples use the Arabic Typesetting font. Compare those examples to more typical fonts:

Rendering of letters depends not only on their place in the word (initial, medial, final) but also on their neighboring letters, i.e. the letter they join with. Each letter has a different appearance in each combination.

Fonts don't always comply with or respect this kind oftuning. To do so, fonts need many glyphs in order to adapt to eachcontext. In more modern typefaces some of these connections are implemented by ligatures, but ligatures can't capture or cover all joining behavior.

In the two left most words, the initial noon differs in that one raises a kind of stroke. This property of raising a stroke is common for a number of letters (beh, teh, noon, theh) which are taller than their connected letters in order to be distinguished in some contexts, such as vs., or to resolve ambiguity. See also3.2.5The so-called teeth letters..

A word shape is composed of not (only) a set of "horizontally" connected letters, but groups of letters (syntagmes).

Figure20 shows syntagmes in two words in a naskh font with many glyph variants.

Compare that with the same words in more plain font:

Group combinations cannot be covered by general or usual ligatures.

Groups of letters may also join vertically (top down) instead of right to left. Not all fonts permit this.

Once again, some fonts try standard ligatures, but this is not ligature. This israther (good) writing practice/style.

One should note that all these features have not only an aesthetic side, but also play a role in justification. Choosing a joining style to suit the desired line width is done at the discretion of authors for hand-written text. Applications should provide general rules to emulate these options, but achieving such justification requires sophisticated algorithms.

Where successive letters have a uniform medial shape, they can be rendered in a way that resembles teeth.

Individual letter shapes may vary according to the context. It's not always the same letters (in red)which raise the stroke inFigure23.

Almost all the writing styles of the Arabic script use a special shape when the letterslam andalef are joined. Most Arabic fonts include mandatory ligatures for this combination. Ignoring this ligature, as shown inFigure24, leads to incorrectly rendered text.

This shape is not limited to the combinationلا [U+0644 ARABIC LETTER LAM +U+0627 ARABIC LETTER ALEF]. Variations of the letteralef such asآ [U+0622 ARABIC LETTER ALEF WITH MADDA ABOVE] andأ [U+0623 ARABIC LETTER ALEF WITH HAMZA ABOVE] when combined with the letterlam follow the same rules. Combination with diacritics does not affect these ligatures. Each of these ligatures also provides a special shape for joining on its right side (to the preceding letter).

More than one diacritic can occur after a single base character and all of them should be visually attached to the same character. Font files usually define special shapes or positioning for combination of diacritics. This extra information should be applied in rendering texts.

Figure25 shows an example, where, according to thisfont’s specification, combining U+0651 ARABIC SHADDA and U+0650 ARABIC KASRA changes their positions. Various font files may require different transformations.

In Arabic script text it is unusual to use diacritics for vowel information and forconsonant lengthening. If they are used, however, there are different approaches to their placement relative to the base characters they modify. Some fonts display short vowel diacritics at the same height, while others vary the height according to the basecharacter.

Another potential difference arises when a short i vowel diacritic is used with a shadda. In some cases the vowel diacritic remains below the base letter, whereas in other cases the vowel diacritic appears above the base letter, but under the shadda (so that it can be distinguished from the short a vowel diacritic, which appears above the shadda).

Every Arabic letter has one, two, or four different joining forms, which allow theletter to join to its neighbors, if applicable. These four forms are:

• Isolated form, used when the letter does not join toany of the surrounding letters;
• Initial form, used when the letter is joining only toits next (left-hand side) letter;
• Medial form, used when the letter is joining on bothsides, and
• Final form, used when the letter is joined only to itsprevious (right-hand side) letter.

Figure26 shows samples of all four joining forms forU+0645 ARABIC LETTER MEEM (م).

We define the following two groups of joining forms:

• Join-to-left forms: either Initial form or Medialform of a letter, which joins to the left-hand side (next) letter. Other forms are callednon-join-to-left.
• Join-to-right forms: either Medial form or Finalform of a letter, which joins to the right-hand side (previous) letter. Other forms arecallednon-join-to-right.

There are different categories of letters based on their joining behavior:

• Dual-joining letters: can join from both sides, like the letter inFigure26, and has all the four shapes mentioned above.
• Right-joining letters: can only join to theirprevious (right-hand side) letter, and therefore, only haveisolated andfinal shapes.Figure27 shows samples of bothforms for U+0631 ARABIC LETTER REH (ر).
• Non-joining letters: cannot join to any surroundingletter, and therefore can only take theisolated form.Figure28 shows a sample of U+0621 ARABIC LETTER HAMZAH (ء) inits only possible form.

Most of Arabic letters are eitherdual-joining orright-joining.

There are core rules on how letters join to each other in the Arabic script, which stay valid regardless of the medium (hand-writing, typewriter, movable-type, digital, etc):

1. Letters of each word join together whenever possible,implicitly.
2. In some languages, like Persian and Urdu, there are words—mostly, but not limited to, compound words—that require explicit breaks in the joining of letters, although joining would otherwise be possible.
3. In certain cases, a letter can be in ajoin-to-left formwithout actually connecting to anything on the left, whether there’s any letter or not.This is often seen in list counters, abbreviations, and other cases where letters do not have a word context, or are taken out of their original word context.
4. In rare cases of words splitting where letters are joined, first letter of the second half will be in ajoin-to-right form without any previous letter. This behavior is limited to special cases like blanking specific letters of a word, line breaks in a paragraph, and word breaks across poetry verses. No standalone word can have any letters injoin-to-right form without joining on the right-hand side.

Figure29 demonstrates how letters join (per Joining Rule1) to form a word.

Arabic letters are represented in their intended joining forms in hand-writing,typewriters, and old (deprecated) digital encodings of the script. In Unicode, letters are encoded semantically—meaning without any information about their joining form—and therefore there’s need for a mechanism for controlling of the joining behavior of the letters.

In Unicode, by default, neighbor Arabic letters join together if and only if bothletters are able to join towards the other.

3.3.4.1Disjoining Enforcement

As noted in Joining Rule 2, sometimes two Arabic letters sit next to each other (inone word) which would normally join together, but should not. In Unicode, for such acase, a special character should be used to enforce disjoining of these letters. Thischaracter is calledU+200C ZERO WIDTH NON-JOINER, orZWNJ for short.

3.3.4.2Joining Enforcement

Similarly, as noted in Joining Rule 4, sometimes an Arabic letter needs to take ajoining form when it would not happen normally. For example, some abbreviation methods use Initial Form of letters, when possible, for every letter in the abbreviation. Again, in Unicode, a special character should be used to enforce joining on this letter. This character is calledU+200D ZERO WIDTH JOINER, orZWJ for short.

BesidesZWJ, there’s another special Unicode character,U+0640 ARABIC TATWEEL, which enforces joining behavior (join causing) onletters next to it. But, in contrast toZWJ,TATWEEL has a glyph shape, looking like a hyphen and usually as wide as the SPACE glyph, which connects to the letters on the main joining line (a.k.a. base-line). So, usingTATWEEL would give a similar Joining Enforcement behavior, but has a side effect of wider length for the letter, which is not always desired. That’s why it’s highly recommended to only useZWJ for joining control.

In Unicode,ZWNJ andZWJ are calledJoining Control Characters.

3.3.4.3Joining-Disjoining Enforcement

Two enforcement methods mentioned above can be combined together to form aJoining-Disjoining Enforcement method, that enablesJoining Rule 3 for cases when there’s adual-joining/right-joining letter after ajoin-to-left letter, whichshould not be joined to its previous letter.

A sequence of letters that join together are called aJoining Segment.Regardless of language,joining segments have no direct relationship tosyllables.

Two types of joining segments exist:closed andopen.

3.3.5.1Closed Joining Segments

Joining Segments usually have a closed form, meaning that they start in anon-join-to-right form and end in anon-join-to-left form.Closedjoining segments are the result of segments either start and end with their normalbehavior (Joining Rule 1), or bydisjoining enforcement (JoiningRule 2).

There are two possible types of closed segments:

• Single-Letter Closed Segment, which contains only one letter that is inits Isolated form.
• Multi-Letter Closed Segment, which contains more than one letter,starting with an Initial form, zero or more Medial forms, and ending with a Finalform.

3.3.5.2Open Joining Segments

Under the certain cases, as noted inJoining Rules 3and 4,joining segments can start with ajoin-to-right form, or end with ajoin-to-left form, or both.

There are three possible types of these segments:

• Open-On-Left Segment, which contains one or moreDual-Joining letters,starting with an Initial form and continuing with zero or more Medial forms.
• Open-On-Right Segment, which starts with zero or more Medial Formletters, and ends with a Final Form letter.
• Open-On-Both-Sides Segment, which contains one or moreDual-Joiningletters, all in their Medial Form.

Arabic Letters, twoJoining Control Characters (ZWNJ andZWJ), andTATWEEL are the only characters used in the Arabic writing system with joining behavior.

Arabic diacritics, other Unicodenon-spacing marks, and most Unicodeformat control characters are consideredtransparent in joining behavior.

All other Unicode characters in Arabic script (as well as Latin and many other majorscripts) are non-joining and do not take any joining forms other than Isolated.

For more the details onArabic Cursive Joining algorithm,please refer to chapterMiddle East-I — Modern andLiturgical Scripts of The Unicode Standard. [UNICODE]

The cursive nature of the Arabic script requires more attention when applying some visual styles to the texts. It mostly occurs when the implementation assumes letters as separated shapes and does not account for cursive scripts.

3.3.7.2Transparency

Arabic fonts achieve joining by overlapping letters. A left-joining letter extends out of its bounding box from the left side and aright-joining letter extends out of its bounding box from the right side. Making each letter transparent can expose theseoverlapping joinings, which should be avoided. Joining the paths of the joined letter into a single shape can remove the overlappings and create the good results.

3.3.7.3Text border

When adding text border, simply adding a border to each letter shape fails to produce the proper result for the Arabic script. A joined letter should not be separated from its joined neighbors by adding border. Like transparency, a way to avoid this is to unify glyph paths into a single big path for all the letters that are joined and add border around that path.

3.3.7.4Styling individual letters

For educational, technical, or even aesthetic reasons, users might want to apply aspecific style to a single letter (or a few letters) in a word. For example,Figure37 is the logo of the largest telecommunications provider in Oman.

This should not break the letter’s joining with its neighbors, as shown inFigure38.

Before entering this section in we need to introduce few preferred terminologicalconventions for disambiguation and simplicity.

• European Numerals are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. They are also referred to asWestern Arabic Numerals or simply asArabic Numerals. Although these are terminologically correct terms, to avoidconfusions we will refrain from using these phrases to refer to these numerals.European Numerals orASCII numerals are used instead.
• Arabic-Indic Numerals are٠,١,٢,٣,٤,٥,٦,٧,٨,٩.
• Eastern Arabic-Indic Numerals are ۰, ۱, ۲, ۳, ۴, ۵, ۶, ۷, ۸, ۹.
• Extended Arabic-Indic Numerals same asEastern Arabic-Indic Numerals.
• Western Arabic Numerals, orArabic Numerals same asEuropean Numerals.
• Eastern Arabic Numerals is used to refer to bothArabic-IndicNumerals andEastern Arabic-Indic Numerals. Should be avoided due toambiguity.
• Indic Numerals should be avoided to refer to either of Arabic-Indic orEastern Arabic-Indic numerals.
• Digit,Numeral digit, andNumeral are used assynonyms.

Three families of numerals are used with languages using the Arabic Script: theEuropean Numerals, theArabic-Indic Numerals, andEastern Arabic-Indic Numerals. The following table, based on asimilar table in [W3-ARAB-MATH] exhibits these three families. Those three numerals which have different shapes betweenArabic-Indic Numerals andEastern Arabic-Indic Numerals are highlighted.

In all Arabic numeral systems, numbers are written with the lowest significant digits to the right and the highest digits to the left (a.k.a. left to right), though Arabic script is written from right to left.

An important fact to note here is thebidirectional category of these numbers.

• European digits andEastern Arabic-Indic digits are of categoryEN (European Number).
• Arabic-Indic digits are of categoryAN (ArabicNumber), differently from their counterpart just above.

The difference in bidirectional category betweenArabic-Indic digits andEastern Arabic-Indic digits is due to the difference in the behavior desired inArabic vs. Persian.

As a consequence, the following sentences, having similar content, result in a very different ordering in a right-to-left context:

European numerals are used with "," (U+002C COMMA) and "." (U+002E FULL STOP) asdecimalseparator andthousands separator, respectively, or vice versa; depending on the region.

• 1.234,5 in Western regions.
• 1,234.5 in Eastern regions.
• Sometimes,U+2009 THIN SPACE orU+202F NARROW NO-BREAK SPACE may also be used asthousands separator.

Arabic-Indic numerals use two specific separators:

• "٫" (U+066B ARABIC DECIMAL SEPARATOR)
• "٬" (U+066C ARABIC THOUSANDS SEPARATOR)
• Example: ١٬٢٣٤٫٥ .

Numbers do not always appear alone, and may appear alongside other characters like financial symbols, fraction signs, decimal and/or thousands signs (excluding math expressions here). Also there are Arabic-specific signs such as؉ [U+0609 ARABIC-INDIC PER MILLE SIGN] and٪ [U+066A ARABIC PERCENT SIGN], as well as the Arabic decimal " ٫ " (U+66B) and thousands  " ٬ " (U+066C) separators, mentioned earlier. These are mostly used with Arabic-Indic digits.

Numerals can also come separated by or mixed with space or other signs. Example are phone numbers +12 34 56 78 89, cars licence plate like 123 د‎ 4,  quantities 37.5°,   ٥٠ كلم (50km) etc.

Particular attention is needed here. Firstly, numbers have a weak directionality with regards to the Bidi algorithm. For example, alongside a number, certain otherwise neutral characters, such as negative/positive sign, currency or degree symbols, are likely to be treated as part of the number rather than a neutral.

Secondly, the placement of the accompanying signs and symbols may depend on the region: generally Middle East (or anglophone) vs. Western (or francophone) regions. This is not to mention punctuation signs.

• The percent sign is placed on the left after the number (ie. ٪١٢ not *١٢٪), and without a space (*٪ ١٢). With European numbers,% [U+0025 PERCENT SIGN] is sometimes used, and can be placed either on the right or the left of the digits (eg. 12% or %12).
• Arabic decimal and thousand separators obey the same rule as for European numbers (١٬٢٣٤٫٥٦). European signs are used with European numbers (1.234,56 or 1,234.56).
• Money or currency signs when they come alongside a number, are placed at the left and treated as part of the number rather than a neutral (€12.3 or €١٢٫٣).
• On the other hand, degree signs are placed at the right of the number (37.5° C, ٩٩٫٥° F) or (37.5° م,۹۹٫۵° ف).
• When indicating quantity, there should a separating space (12 كغ,٤٥ مم).
• The same rule applies when using range of values. (12-15 كغ, but12٪-15٪ كغ).
• / [U+002F SOLIDUS] is used for fractions or ratio notation. Fractions are noted for one-half, say, 2/1 or ٢/١, mostly in RTL mode. There is no standard approach, however, and some region/author may write 1/2 for European digits.
• Notation with Solidus sign " / " are used in:
  
  • Notation such as speed "50 km/h"
    كم/س ‎ 50
  • Notation such as "Page / Volume", for example a reference to a page in a volume
    ١٢٣/١ for volume ١, page ١٢٣
  • or reference to Quran "Verse / Surah",
    ١٣/٩٠ for Surah 90, Verse 13
  • Mark or rank in a classification
    20/15 for rank 15 over 20
  • Dates (2017/06/24, ٢٠١٧/٠٦/٢٤)

This is the same mechanism widely used when justifying Latin scripts, where the width of the spaces between the words can be increased or decreased to change the width of the line.

A minimum width is defined for how much the space can be shrunk, because putting the words too close to each other creates aesthetic and legibility problems.

Stretching the space too wide is also undesirable, but is utilized as a last resort when it is not possible to use other solutions to make fully justified paragraphs. In some applications a maximum width for the inter-word space is defined as a soft limit (compared to minimum width which is a hard limit). Reaching the maximum width makes the software to try to use other solutions for justification. If no other solution could yield the requiredresult, the software would fall back to inter-word spacing and stretch the space past the maximum width.

Depending solely on this mechanism for aligning lines in a justified paragraph can lead to unpleasant results, such as rivers (multiple stretched spaces appearing vertically close to each other and forming a white gap inside the paragraph) and uneven distribution of color in the paragraph. Hence, typographers generally use other mechanisms as well to minimize the effect of adjusting inter-word spaces.

This solution alters the space between letters of each word to change the width of the text. Like adjusting inter-word spaces, this is used for Latin scripts as well, but using it for Arabic script involves considerations specific to Arabic. As noted inJoining and Intra-Word Spaces, the principal consideration is that gaps between characters only exist for those letters that join only to the right, such asdal andreh . Adjustment of intra-word space is not relevant where one letter is joined to its neighbors.

Depending on the writing style and the typeface in use, different amounts of alteration to the intra-word space is acceptable for Arabic. Some writing styles allow more liberal adjustments to the closeness of the letter groups, while others can only accept small adjustments in this regard. In any case, much smaller adjustments can be used for intra-word spacing in comparison for inter-word spacing, which naturally is wider and tolerate bigger adjustments.

In addition to the four joining forms (isolated, initial, medial, and final), each Arabic letter can come with different shapes while preserving its joining form. For instance, a typeface or writing style can offer two or more shapes for the final form of a single letter.

These variant shapes usually have variant widths and hence can be used to adjust the width of the line.

An advantage of using alternative letter shapes when justifying paragraphs is that it does not involve modifying default properties of the typeface (width of space or other characters). Instead, it is using shapes that are part of the typeface and are in harmony with other shapes in the lines.

But excessive use of alternative shapes, such as using multiple very wide alternatives close to each other, can create unnatural results.

It is not possible to justify paragraphs using only alternative letter shapes, because these shapes have predefined widths. For example, if a line should get 25 points wider, it is impossible to achieve that by using alternative letter shapes that are, say, 10 or 20 or 30 points wider than the default shapes. But these shapes can make the lines closer to measure, thus reducing the usage of other mechanisms.

Some Arabic fonts, following the writing styles that use special shapes when joining certain letters, provide a rich number of ligatures. These ligatures can be used in paragraph justification, since they usually reduce the widths of the words.

But existence of the ligatures in a font does not mean that they can be used freely. A font may provide some of its ligatures for creating an artistic style, which would be unsuitable for texts requiring optimum legibility.

For that reason, the user should be able to select which sets of ligatures can be used for justification. Fonts can offer predefined sets of ligatures to simplify this process.

Kashida refers to extending the horizontal connection between joined letters.

This is a feature deeply related with the cursive nature of Arabic script. Kashida is an interesting tool for paragraph justification. It is more flexible than alternative letter shapes and ligatures, because it is not restricted to a limited number of predefined widths. At the same time, it has relatively less effect on the text color than spacing.

But a proper implementation of kashida involves a number of limitations and considerations.

Excessive use of kashida or applying very long kashidas results in uneven color. Also, horizontal or vertical proximity of numerous kashida creates an unnatural color.

Kashida is not always straight. Some fonts may require curvilinear kashidas, which require more advanced implementations.

Typographers can have preferred places for applying kashidas. In other words, instead of applying kashida between every joined pair of letters, they want it at certain joins.

Another preference is avoiding multiple kashidas in a single word.

Tatweel is adual-joining character that can be inserted between two joined letters to widen their connection. In The Unicode Standard, tatweel is represented asـ [U+0640 ARABIC TATWEEL].

Tatweel extends letter connections in a fashion similar to kashida, but in a much more limited way. It is a character that has to be in the text or inserted like other characters. It has a predefined width, like any other character.

Yet it is much simpler to implement, since it acts like normal Arabic characters and does not require special treatment. For this reason, it can be considered useful specially in constrained implementations like fixed-width environments.

Each of the above six mechanisms have their own limitations and side effects. Utilizing only one of them for justifying paragraphs can create undesirable results. Multiple mechanisms can be used at the same time to work around their limitations and minimize their side effects.

Since Arabic provides various mechanisms that can be used for justification, an advanced implementation that supports all or most of the above features can produce exemplary justifications. More limited applications can combine what is available.

Preferences for each mechanisms can depend on the document and text and the preference of the typographers and users. Implementations can enable users to prioritize and control the mechanisms mentioned above.