Arabic and Persian Gap Analysis

W3C Working Draft

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Shervin Afshar (Netflix)
Richard Ishida (W3C)
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This document describes and prioritises gaps for the support of Arabic and Persian languages on the Web and in eBooks. In particular, it is concerned with text layout. It checks that needed features are supported in W3C specifications, in particular HTML and CSS and those relating to digital publications. It also checks whether the features have been implemented in browsers and ereaders. This is a preliminary analysis.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at

This document describes and prioritises gaps for the support of Arabic and Persian languages on the Web and in eBooks. In particular, it is concerned with text layout. It checks that needed features are supported in W3C specifications, in particular HTML and CSS and those relating to digital publications. It also checks whether the features have been implemented in browsers and ereaders. This document complements the document Text Layout Requirements for the Arabic Script, which describes the requirements for areas where gaps appear. It is linked to from the language matrix that tracks Web support for many languages.

The editor's draft of this document is being developed by the Arabic Layout Task Force, part of the W3C Internationalization Interest Group. It is published by the Internationalization Working Group. The end target for this document is a Working Group Note.

This document was published by the Internationalization Working Group as a Working Draft.

GitHub Issues are preferred for discussion of this specification.

Publication as a Working Draft does not imply endorsement by the W3C Membership.

This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 1 August 2017 W3C Patent Policy. The group does not expect this document to become a W3C Recommendation. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 15 September 2020 W3C Process Document.

1. Introduction

The W3C needs to make sure that the needs of scripts and languages around the world are built in to technologies such as HTML, CSS, SVG, etc. so that Web pages and eBooks can look and behave as people expect around the world.

This page documents difficulties people encounter when trying to use the Arabic and Persian languages in the Arabic script on the Web.

Having identified an issue, it investigates the current status with regards to web specifications and implementations by user agents (browsers, e-readers, etc.), and attempts to prioritise the severity of the issue for web users.

A summary of this report and others can be found as part of the language matrix.

1.1 Work flow

This version of the document is a preliminary analysis

Gap analysis work usually starts with a preliminary analysis, conducted quickly by one or a small group of experts. Then a more detailed analysis is carried out, involving a wider range of experts. The detailed analysis may involve the development of tests, in order to illustrate issues and track results for browsers. The next phase is ongoing maintenance. It is expected that the resulting document will not be frozen: as gaps are fixed, this should be noted in the document. It is also possible that new gaps are noticed or arise, and they can be added to this document when that happens.

As the gap analysis develops, the requirements for features that are problematic should be described in the companion document, Text Layout Requirements for the Arabic Script. Links to the appropriate part of that document should be added to this document as the material is created. Note that the requirements document should not contain any technology-specific information: all of that belongs here.

1.2 Prioritization

This document not only describes gaps, it also attempts to prioritise them in terms of the impact on the local user. The prioritisation is indicated by colour.


It is important to note that these colours do not indicate to what extent a particular features is broken. They indicate the impact of a broken or missing feature on the content author or end user.

Basic styling is the level that would be generally accepted as sufficient for most Web pages. Advanced level support would include additional features one might expect to include in ebooks or other advanced typographic formats. There may be features of a script or language that are not supported on the Web, but that are not generally regarded as necessary (usually archaic or obscure features). In this case, the feature can be described here, but the status should be marked as OK.

The decision as to what priority level is assigned to a described gap is down to the experts doing the gap analysis. It may not always be straightforward to decide. If a given section in this document refers to more than one feature that is broken, each with different impacts on Web users, the priority for the section should be the lowest denominator.

A cell can be scored as OK if the feature in question is specified in an appropriate specification, and is supported by user agents. A specification that is in CR or later and has two implementations in 'major' browsers will count. This means that the feature may not be supported in all browsers yet. (At some point in the future we may try to distinguish, visually, whether support is available in a specification but still pending in major browsers or applications.)

2. Text direction

See also General page layout & progression for features such as column layout, page turning direction, etc. that are affected by text direction.

2.1 Vertical text

Are the script requirements for vertically oriented text met? What about if you mix vertical text with scripts that are normally only horizontal? Do you need a switch to use different characters in vertical vs. horizontal text? Does the browser support short runs of horizontal text in vertical lines (tate-chu-yoko in Japanese) as expected? Is the orientation of characters and the directional ordering of characters supported as needed? See available information or check for currently needed data.

We need to clarify whether there is a particular requirement for handling arabic text specially in vertical lines, such as upright glyphs. We are also waiting on implementation of sideways values of writing-modes in order to be able to effectively use arabic text in vertical arrangements (such as book spines, table headings, etc), but that is not a problem specific to arabic.

#242 Vertical text in spines, etc.

This issue is applicable to most languages.

Vertical text may occur for special effects (the spine of a book, table column headings, etc). Typographically, it is simply horizontal text that is rotated. The CSS feature defined in Writing Modes Level 4, which is in CR, offers a solution using sideways-lr|sideways-rl values of the writing-mode property.

The feature isn't supported yet by Chrome or Safari. Firefox does support it.

Test: sideways-rl/lr is supported in browsers

Browser bugs raised: Chromium, WebKit

2.2 Bidirectional text

If this script runs right-to-left, are there any issues when handling that? Is bidirectional text adequately supported? What about numbers and expressions? Do the Unicode bidi controls and HTML markup provide the support needed? Is isolation of directional runs problematic? See available information or check for currently needed data.

#244 Support for isolating formatting characters lacking in some browsers

This issue is common to all RTL scripts.

Webkit still doesn't support RLI, LRI, PDI and FSI formatting characters, although there has been progress elsewhere recently due to Blink adding support, and Edge moving to Blink. Firefox also supports these characters.

Tests & results: Isolating formatting characters

The behaviour of these characters is described in the Unicode Standard. See also How to use Unicode controls for bidi text.

Related browser bug: Webkit

#217 Logical CSS keyword support needed

This issue is common to all RTL scripts.

Adoption of logical keywords such as -start and -end, rather than -left and -right needs to be completed.

For margins, padding, block size, border colour, width & style, logical keywords such as margin-inline-start or margin-block-end are widely supported by major browsers in their simplest forms (such as those just mentioned). However, logical properties are not well supported in shorthands such as margin-block or margin-inline or the margin property. The lack of support for shorthands is significant, since they are expected to have high use.

Support for the margin shorthand is currently held up by a discussion about the appropriate syntax. See this CSS issue.

Other logical properties that are not widely supported include border radius, caption side, and float. Firefox does support border-radius and floats, but otherwise these are not supported.

See a set of test results.

These new values also need to be widely supported in editing applications.

#216 Base direction needed for string data

This issue is common to all RTL scripts.

When strings are passed around, some applications don't receive or use information about the appropriate base direction to use for those strings when they are rendered as part of a page.

This can lead to text being incorrectly aligned, and to text within a sentence or paragraph being incorrectly ordered. Some of this can be addressed by using heuristics to detect the direction first-strongly directional character in the string, but some strings can fail such heuristics.

For example, imagine a service which retrieves book names on an English page. If the page retrieves from the database an Arabic book name that begins with LTR letters, it should look like this:

Screenshot 2021-01-21 at 18 12 42

However, if just first-strong heuristics are used to decide the base direction for the inserted book name, it will incorrectly produce:

Screenshot 2021-01-21 at 18 14 00

Typically, for these cases the databases or JSON files, etc., from which such strings are pulled do not contain metadata about appropriate direction which could be used to correct the display.

The W3C Internationalization activity is working to help specification developers to address this issue. See Strings on the Web: Language and Direction Metadata.

3. Characters and phrases

3.1 Characters & encoding

Are there any character repertoire issues preventing use of this script on the Web? Do variation selectors need attention? Are there any other encoding-related issues? See available information or check for currently needed data.

3.2 Fonts

Do the standard fallback fonts used in browsers (eg. serif, sans-serif, cursive, etc.) match expectations? Are special font or OpenType features needed for this script that are not available? See available information or check for currently needed data.

3.3 Font styles, weight, etc

This covers ways of modifying the glyphs, such as for italicisation, bolding, oblique, etc. Do italic fonts lean in the right direction? Is synthesised italicisation problematic? Are there other problems relating to bolding or italicisation - perhaps relating to generalised assumptions of applicability? See available information or check for currently needed data.

#218 Controls needed for italic slant direction

There should be means available to control the direction in which 'italicised' or 'oblique' text slants, since in some schools of Arabic script typography, text in these styles need to slant to the left.

See the example just below the large letters in this newspaper masthead.


3.4 Glyph shaping and positioning

Does the script in question require additional user control features to support alterations to the position or shape of glyphs, for example adjusting the distance between the base text and diacritics, or changing the glyphs used in a systematic way? Do you need to be able to compose/decompose conjuncts, or show characters that are otherwise hidden, etc? See available information or check for currently needed data.

#219 Controls needed to adjust diacritic positioning

For advanced typographic purposes, the fixed position of diacritical marks relative to base letter or baseline and the logical stacking behavior of them might not be sufficient. Therefore, it should be possible to adjust the positioning and combining order and changes to the individual marks when combining. Fonts and other systems may implement the logic needed to result in an optimal presentation of diacritical mark clusters by default.

3.5 Cursive text

If this script is cursive (eg. Arabic, N’Ko, Syriac, etc), are there problems or needed features related to the handling of cursive text? Do cursive links break if parts of a word are marked up or styled? Do Unicode joiner and non-joiner characters behave as expected? See available information or check for currently needed data.

#222 Inline elements break cursive shaping

This issue is applicable to text in all cursive scripts.

When elements surround part of a cursive run of text, and apply styling, the results often break the cursive joins. (See the results of trying to colour individual letters in the illustration below – as expected above, unsuccessful below.)

Screenshot 2021-01-22 at 15 19 49


After some discussion, the CSS spec requires the following:

  1. Markup alone around part of a joined up sequence must not disturb the joining behaviour.
  2. Styling that doesn't affect the characters, such as text-decoration, must not break the joins.
  3. Styling that does affect the shape of the characters should not break the joins, however the result is not well defined for complex glyph arrangements such as ligatures where the markup occurs between characters that make up the ligature.
  4. Non-zero margins, padding, and borders, will break the join, as will isolation boundaries.

See the tests and results for a range of different styling effects. Here is a quick interactive test for colour change.

Webkit breaks cursive joining as soon as markup appears around a character, and so obviously fails for any type of styling application, too.

Gecko, and Blink (and Legacy Edge) keep joins for styling that doesn't affect the shape of the characters (eg. text-decoration), and keeps it for colour changes, however they fail for changes in font-weight, font-style, and font-size, as well as for markup such as em and b tags.

It would be useful to decide on the potential impact of the failures described here, so as to prioritise the issue. Is the inability to surround/style parts of a word a significant issue? It may be problematic when defining a term (using dfn) if the term is only part of the run of letters between spaces, eg. after the definite article.

#221 Text opacity shows glyph overlap

This issue is likely to apply to all cursive script text.

When opacity is applied to text, Gecko and Blink produce dark patches where the cursive glyphs overlap, but Webkit and Legacy Edge don't. See the test.


The CSS Fonts spec was updated 2020-07-27 to clarify that opacity should be applied to a whole element, not to individual letters, so that this shouldn't happen.

#220 Text stroke cuts joining glyphs apart

This issue is likely to apply to all cursive script text.

The property text-stroke is not yet in CSS, but has been implemented in major browsers under the name -webkit-text-stroke. In all major browser engines, the stroke around the text interrupts the cursive flow.


See tests & results in the i18n test suite.

-webkit-text-stroke is currently specified in

3.6 Baselines, line-height, etc

Does the browser support requirements for baseline alignment between mixed scripts and in general? See available information or check for currently needed data.

3.7 Transforming characters

Does your script need special text transforms that are not supported? Does your script convert letters to uppercase, capitalised and lowercase alternatives according to your typographic needs? Do you need to to convert between half-width and full-width presentation forms? See available information or check for currently needed data.

3.8 Grapheme/word segmentation & selection

This is about how text is divided into graphemes, words, sentences, etc., and behaviour associated with that. Do Unicode grapheme clusters appropriately segment character units for your script? When you double- or triple-click on the text, is the expected range of characters highlighted? When you move through the text with the cursor, or backspace, etc. do you see the expected behaviour? (Some of the answers to these questions may be picker up in other sections, such as line-breaking, or initial-letter styling.) See available information or check for currently needed data.

Arabic script word boundaries, similar to Latin script, generally can be distinguished by white space and a specific subset of punctuations. There are few exceptions which are listed in Arabic Layout Requirement document.

To enforce a disjoining behavior between the letters which under circumstances of their position normally join, special Unicode character U+200C ZERO WIDTH NON-JOINER (ZWNJ) is used. This usage is detailed in Arabic Layout Requirement document.

All major desktop browsers select a whole word when you double-click on it, including when the word contains ZWNJ. Single-letter prepositions attached to the word are also selected. See some tests.

3.9 Inline features & punctuation

Are there specific problems related to punctuation or the interaction of the text with punctuation (for example separation of punctuation from previous text, but allowing no line break between)? Are there issues related to handling of abbreviation, ellipsis, or iteration? Are there problems related to bracketing information or demarcating things such as proper nouns, etc? See available information or check for currently needed data.

3.10 Text decoration

This is about ways of marking text (see also specific sections dedicated to quotations and inline notes/annotations). Is it possible to express emphasis or highlight content as expected? Bold, italic and under-/over-lines are not always appropriate, and some scripts have their own unique ways of doing things, that are not in the Western tradition at all. Text delimiters mark certain items or sections off from the main text, such as book names in Chinese, quotations, head markers in Tibetan, etc, and often involve the use of punctuation. Is there any behaviour that isn't well supported, such as overlines for numeric digits in Syriac? Are there issues about the positioning or use of underlines? Some aspects related to the drawing of lines alongside or through text involve local typographic considerations. Do underlines need to be broken in special ways for this script? Do you need support for additional line shapes or widths? Does the distance or position of the lines relative to the text need to vary in ways that are not achievable? Are lines correctly drawn relative to vertical text? See available information or check for currently needed data.

#223 Underlines too close to text

It must be possible to position under- and overlines further away from the baseline than for Latin text, because ascenders and descenders are longer in many Arabic script fonts. It is common for underlines in Arabic text to be low enough to avoid crossing the ink of descenders in the content, however there are also examples of printed text where ink is skipped – however the underline is still usually further from the baseline than, for example, Latin text. See the discussion in this issue. The main requirement that seems clear at the moment is that there needs to be a way of adjusting the positioning of the underline to move it further away from the baseline than is currently possible on the Web.

For underlines, the CSS Text Decoration spec describes 2 properties that can help with this.

text-underline-position is described in Level 3 (CR) and has the value under. This value positions underline under the element’s text content so that it usually does not cross the descenders. However, a note in the spec says that it does not guarantee that the underline will not conflict with glyphs, as some fonts have descenders or diacritics that extend below the font’s descent metrics.

text-underline-offset is described in Level 4 (WD) and allows you to specify the distance from the text-underline-position as auto, as a fixed distance, or as a percentage of of 1em. As long as you pair this with the font you are using (to make appropriate adjustments) this can be effective in positioning the underline appropriately.

See tests.

Currently text-underline-offset is not supported by Blink, or Webkit, but is supported by Gecko.

text-underline-position often produces sufficient clearance, depending on the font, and is supported by Gecko and Webkit, but not by Blink.

See the Chromium bug for text-underline-offset.

3.11 Quotations

Are there any issues when dealing with quotations marks, especially when nested? Should block quotes be indented or handled specially? See available information or check for currently needed data.

#224 q element produces incorrect quotation marks when language changes

When an Arabic or Persian page contains a quotation in another language, the quotation marks used around that quotation (and inside it for embedded quotes) should be the Arabic or Persian ones – not those of the language of the quotation.

Currently, if the language of the quotation is declared on the q tag in HTML using the lang attribute, browsers instead set the quotation marks based on the language of the quote.

For example, if English text is quoted in a Persian sentence surrounded by just <q>, the quotation marks will be correct:

یک «two ‹three›».

However, if lang="en" is added to the q tag, the result becomes:

یک “two ‘three’”.

Here is a test. There are also tests and results in the i18n test suite.

This incorrect behaviour is currently dictated by the HTML specification, so an issue has been raised to change the spec.

3.12 Inline notes & annotations

The ruby spec currently specifies an initial subset of requirements for fine-tuning the typography of phonetic and semantic annotations of East Asian text, including furigana, pinyin and zhuyin fuhao systems. Is is adequate for what it sets out to do? What other controls will be needed in the future? What about other types of inline annotation, such as warichu? (For referent-type notes such as footnotes, see below.) See available information or check for currently needed data.

3.13 Data formats & numbers

If the script has its own set of number digits, are there any issues in how they are used? Does the script or language use special format patterns that are problematic (eg. 12,34,000 in India)? What about date/time formats and selection - and are non-Gregorian calendars needed? Do percent signs and other symbols associated with number work correctly, and do numbers need special decorations, (like in Ethiopic or Syriac)? How about the management of personal names, addresses, etc. in web pages: are there issues? See available information or check for currently needed data.

Internationalization software libraries identify Arabic-Indic numerals as the set of numerals which should be used with text in Arabic language excluding a number of Arabic-speaking countries of Northern and Northwestern Africa which should use Arabic (ASCII) numerals. Surveys of publications, monetary and governmental documents, and manuscripts confirm these precedences. However, there is a considerable diverging trend from these recommendations observable on the web, digital products, and in user-generated content. If not considered in design and implementation of software products dealing with Arabic text, this discrepency could be potentially disadvantageous to the quality of text layout, digital typography, and locale-specific data processing.

4. Lines and Paragraphs

4.1 Line breaking

Does the browser capture the rules about the way text in your script wraps when it hits the end of a line? Does line-breaking wrap whole 'words' at a time, or characters, or something else (such as syllables in Tibetan and Javanese)? What characters should not appear at the end or start of a line, and what should be done to prevent that? See available information or check for currently needed data.

4.2 Hyphenation

Is hyphenation used for your script, or something else? If hyphenation is used, does it work as expected? (Note, this is about line-end hyphenation when text is wrapped, rather than use of the hyphen and related characters as punctuation marks.) See available information or check for currently needed data.

There is no hyphenation in Arabic or Persian language text.

4.3 Text alignment & justification

When text in a paragraph needs to have flush lines down both sides, does it follow the rules for your script? Does the script need assistance to conform to a grid pattern? Does your script allow punctuation to hang outside the text box at the start or end of a line? Where adjustments are need to make a line flush, how is that done? Do you shrink/stretch space between words and/or letters? Are word baselines stretched, as in Arabic? What about paragraph indents, or the need for logical alignment keywords, such as start/end, rather than left/right? See available information or check for currently needed data.

#225 Need better control of justification mechanisms

For justification of Arabic script text, there are various common strategies available. These could be categorized in two major groups; strategies based on adjusting inter-word or inter-character whitespace and strategies based on adjusting the letterforms.

A basic implementation must provide at least one of these strategies for adequate justification results. Advanced implementations should provide users with the necessary means to control the selection of strategies, adjustment of their attributes, and the priority with which they are being applied.

Currently, CSS specifications do not provide these advanced features, but recommend that the implementations select the justification strategy appropriate to the text.

Arabic Layout Requirement document includes a section dedicated to this topic.

4.4 Letter spacing

Some scripts create emphasis or other effects by spacing out the words, letters or syllables in a word. Are there requirements for this script/language that are unsupported? (For justification related spacing, see below.) See available information or check for currently needed data.

#226 Need control of baseline stretching

It is very common in Arabic script to stretch words or phrases to a particular width (eg. to match a Latin translation or transcription above or below). This is achieved by lengthening the connections between letters, and to some extent by use of wide glyph variants, etc. The rules for which part of the text to stretch and how far are complicated - this is not the even spacing that usually occurs in tracked Latin text. There are currently no mechanisms for managing this process effectively in HTML/CSS.

4.5 Lists, counters, etc.

The CSS Counter Styles specification describes a limited set of simple and complex styles for counters to be used in list numbering, chapter heading numbering, etc.The rules plus more counter styles (totalling around 120 for over 30 scripts) are listed in the document Ready-made Counter Styles. Do these cover your needs? Are the details correct? Are there other aspects related to counters and lists that need to be addressed? See available information or check for currently needed data.

#227 Add support for custom counter-styles

Arabic script text uses local counter styles. While some of these are supported by some browsers, the set of symbols used and their order varies by language. Custom counter styles can be created using Firefox only. The CSS spec needs to become a Rec and more browsers need to support it.

4.6 Styling initials

Does the browser or ereader correctly handle special styling of the initial letter of a line or paragraph, such as for drop caps or similar? How about the size relationship between the large letter and the lines alongide? where does the large letter anchor relative to the lines alongside? is it normal to include initial quote marks in the large letter? is the large letter really a syllable? etc. Are all of these things working as expected? See available information or check for currently needed data.

Although initial letter styling is not an innate feature of the Arabic script, there have been occurences of its usage noted. However, the specifications and guidelines for composition of these decorative elements are undefined or insubstantial; for example, which of the joining forms of letters is to be used or how the joining behaviour is treated accross the boundary between the styled initial letter and rest of the paragraph.

5. Page & book layout

5.1 General page layout & progression

How are the main text area and ancilliary areas positioned and defined? Are there any special requirements here, such as dimensions in characters for the Japanese kihon hanmen? The book cover for scripts that are read right-to-left scripts is on the right of the spine, rather than the left. Is that provided for? When content can flow vertically and to the left or right, how do you specify the location of objects, text, etc. relative to the flow? For example, keywords 'left' and 'right' are likely to need to be reversed for pages written in English and page written in Arabic. Do tables and grid layouts work as expected? How do columns work in vertical text? Can you mix block of vertical and horizontal text correctly? Does text scroll in the expected direction? Other topics that belong here include any local requirements for things such as printer marks, tables of contents and indexes. See available information or check for currently needed data.

5.2 Footnotes, endnotes, etc.

Does your script have special requirements for footnotes, endnotes or other necessary annotations of this kind in the way needed for your culture? (There is a section above for purely inline annotations, such as ruby or warichu. This section is more about annotation systems that separate the reference marks and the content of the notes.) See available information or check for currently needed data.

5.3 Page headers, footers, etc.

Are there special conventions for page numbering, or the way that running headers and the like are handled? See available information or check for currently needed data.

5.4 Forms & user interaction

Are vertical form controls well supported? In right-to-left scripts, is it possible to set the base direction for a form field? Is the scroll bar on the correct side? etc. See available information or check for currently needed data.

6. Other

6.1 Culture-specific features

Sometimes a script or language does things that are not common outside of its sphere of influence. This is a loose bag of additional items that weren't previously mentioned. This section may also be relevant for observations related to locale formats (such as number, date, currency, format support).

6.2 What else?

There are many other CSS modules which may need review for script-specific requirements, not to mention the SVG, HTML, Speech, MathML and other specifications. What else is likely to cause problems for worldwide deployment of the Web, and what requirements need to be addressed to make the Web function well locally?

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