Status of This Document
This section describes the status of this
document at the time of its publication. A list of current W3C
publications and the latest revision of this technical report can be found
in the
W3C standards and drafts index at
https://www.w3.org/TR/.
This document describes and prioritises gaps for the support of the Tamil script 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.
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 in the GitHub repository Indian Language Enablement (ilreq), with contributors from 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 Group Draft Note using the
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This is a draft document and may be updated, replaced, or obsoleted by other
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This document is governed by the
03 November 2023 W3C Process Document.
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 that people encounter when trying to use languages written in the Tamil 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.
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.
Key:
It is important to note that these colours do not indicate to what extent a particular feature is broken. They indicate the impact of a broken or missing feature on the content author or end user.
A cell can be scored as OK if the feature in question is specified in an appropriate specification (including Candidate Recommendations), and is supported by at least two major browser engines.
Advanced level support includes features that one might expect to include in ebooks or other advanced typographic formats. If a feature of a script or language is not supported on the Web, but is not generally regarded as necessary (usually archaic or obscure features), even if the feature is described here, the status may 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 will be the lowest denominator.
See also General page layout & progression for features such as column layout, page turning direction, etc. that are affected by text direction.
In what direction does text flow along a line and across a page? (If the basic direction is right-to-left see 3.2 Bidirectional text.) If the script uses vertically oriented text, what are the requirements? 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?
GitHub issue #70
Languages: hi bn ta gu pa 2
This issue is applicable to many Indian languages.
When upright characters appear in vertical lines of text, browsers need to tailor grapheme cluster rules so that full orthographic syllables represented as conjuncts, are kept together.
See requirements at: Indic Layout Requirements, but add to those the points made in Typographic character units in complex scripts.
Gecko appears to segment on grapheme clusters. Blink, and Webkit keep conjuncts together. But all engines have problems with vowel-signs, especially but not only pre-base vowel-signs.Marked as advanced, since vertical text is not a common use case. In writing sytems like modern Tamil, it is even less common, since conjuncts are rarely used.Interactive test, When devanagari characters are rendered upright in vertical text, orthographic syllables containing conjuncts are kept together
Gecko • Blink • Webkit
All three major desktop browsers now keep the conjuncts together, however the vowel signs attached to those orthographic syllables are not kept with the rest of the syllable.
If the general inline direction is right-to-left, are there any issues when handling that? Where the inline direction of text is mixed, is this 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?
How are fonts grouped into recognisable writing styles? How is each writing style used? Do the standard fallback fonts used in browsers (eg. serif, sans-serif, cursive, etc.) match expectations? Or are additional generic font styles needed? Are special font or OpenType features needed for this script that are not available? What other general, font-related issues arise? The font styles described here refer to alternative types of writing style, such as naskh vs nastaliq; for oblique, italic, and weights see instead 4.3 Letterform slopes, weights, & italics.
If context-sensitive rendering support is needed to shape combinations of letters or position certain glyphs relative to others, is this adequately provided for? 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 ligatures, or show characters that are otherwise hidden, etc? If text is cursive, see the separate section 4.4 Cursive text.
If this script is cursive (ie. letters are generally joined up, like in 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?
Most languages are now supported by Unicode, but there are still occasional issues. In particular, there may be issues related to ordering of characters, or competing encodings (as in Myanmar), or standardisation of variation selectors or the encoding model (as in Mongolian). 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?
This is about how text is divided into graphemes, words, sentences, etc., and behaviour associated with that. Are there special requirements for the following operations: forwards/backwards deletion, cursor movement & selection, character counts, searching & matching, text insertion, line-breaking, justification, case conversions, sorting? Are words separated by spaces, or other characters? Are there special requirements when double-clicking or triple-clicking on the text? Are words hyphenated? (Some of the answers to these questions may be picked up in other sections, such as 7.1 Line breaking & hyphenation, or 7.6 Styling initials.)
GitHub issue #89
Languages: hi bn ta gu pa 2
If you try to style part of a syllable by putting a span around the characters you want to style, the overall shape of the syllable is broken.
Here are a number of examples:
- Devanagari. If you put a span around the first two characters of the 3-character syllable स्तिठड (eg. in order to color or otherwise style it), the i vowel-sign no longer appears at the start of the word, but looks like it modifies the next character (ठ).
- Gujarati. If you put a span around the ન્ડ two characters of the 3-character syllable ન્ડિ in ઇન્ડિય (eg. in order to color or otherwise style it), the i vowel-sign no longer appears at the start of the word, but looks like it modifies the next character (ય).
- Bengali. If you put a span around the ব first character of the two character syllable বি in বিভাগের (eg. in order to color or otherwise style it), the vowel-sign no longer appears at the start of the word, but looks like incorrect inputting at the wrong place.
- Tamil. If you put a span around the ம first character of the two character syllable மொ in மொழி (eg. in order to color or otherwise style it), the half part of o vowel-sign no longer appears at the start of the word, but looks like incorrect inputting at the wrong place.
Apparently this requirement is a bit difficult to cater to as it requires the knowledge to be transferred by the font to the rendering engine about which part of the glyph is attributed to which code-point in storage. However, if it can be achieved, nothing like it.
GitHub issue #72
Languages: ta 1
The Unicode concept of 'grapheme cluster' currently fails to represent the small number of conjuncts that are used in modern Tamil, ie. kṣa க்ஷ and the two alternative sequences for srī, ஶ்ரீ and ஸ்ரீ. This means that various editing operations, line breaking algorithms, vertical text, etc. are liable to break text at the wrong point when those conjuncts are used. For more details, see the relevant sections.
Indic Layout Requirements provides a grammar for indian orthographic syllable boundaries which works for the consonant clusters in Tamil which don't use conjuncts.
Specs:
CSS uses the concept of 'typographic character unit', rather than grapheme cluster, in its specs with the explanation that these cases are beyond the scope of the grapheme cluster concept and that implementations should provide appropriate support.
What characters are used to indicate the boundaries of phrases, sentences, and sections? What about other punctuation, such as dashes, connectors, separators, etc? Are there specific problems related to punctuation or the interaction of the text with punctuation (for example, punctuation that is separated from preceding text but must not be wrapped alone to the next line)? Are there problems related to bracketing information or demarcating things such as proper nouns, etc? Some of these topics have their own sections; see also 6.2 Quotations & citations, and 6.4 Abbreviation, ellipsis & repetition.
This is a subtopic of phrase & section boundaries that is worth handling separately. What characters are used to indicate quotations? Do quotations within quotations use different characters? What characters are used to indicate dialogue? Are the same mechanisms used to cite words, or for scare quotes, etc? What about citing book or article names? Are there any issues when dealing with quotations marks, especially when nested? Should block quotes be indented or handled specially? Do quotation marks take text direction into account appropriately?
How are emphasis and highlighting achieved? If lines or marks are drawn alongside, over or through the text, do they need to be a special distance from the text itself? Is it important to skip characters when underlining, etc? How do things change for vertically set text?
What characters or other methods are used to indicate abbreviation, ellipsis & repetition? Are there problems?
What mechanisms, if any, are used to create *inline* notes and annotations? Are the appropriate methods for inline annotations supported for this script? 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? This section deals with inline annotation approaches. For annotation methods where a marker in the text points out to another part of the document see 8.3 Footnotes, endnotes, etc..
This section is a catch-all for inline features that don't fit under the previous sections. It can also be used to describe in one place a set of general requirements related to inline features when those features appear in more than one of the sections above. It covers characters or methods (eg. text decoration) that are used to convey information about a range of text. Are all needed forms of highlighting or marking of text available, such as wavy underlining, numeric overbars, etc. If lines are drawn alongside, over or through the text, do they need to be a special distance from the text itself? Is it important to skip characters when underlining, etc? How do things change for vertically set text? Are there other punctuation marks that were not covered in preceding sections? Are lines correctly drawn relative to vertical text?
GitHub issue #90
Languages: hi bn ta gu pa 1
Indian language text has some signs called as Matras which sometimes join above the shirorekha or below the normal baseline.
Applications should ensure that the underline and overline when getting rendered, should adaquetly be taken into consideration. Chrome browser seemed to be perfectly rendering the underline and overline feature by breaking the same where a matra occurs. Internet Explorer also handles it a bit differently by appropriately lowering or heightening the respective lines.
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? 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.)
GitHub issue #79
Languages: ta 1
None of the major browsers support Tamil hyphenation out of the box. This is a problem for text in narrow columns, because Tamil words tend to be long.
In the case of Tamil, simple dictionary lookup is not enough, because the language is highly inflexional and a significant element of morphological analysis is needed in addition to other Tamil-specific orthographic rules for placement of break opportunities.
Tamil also needs to hyphenate without adding a visual marker, as shown in the picture where yellow text indicates hyphenated words that have been wrapped.
Specs:
css-text-3 provides the hyphens property, but browsers need to implement the actual mechanism for processing the text.
(It is possible to produce manual hyphenation, but given the number of words that need to be hyphenated in a typical Tamil text, this isn't going to be very useful. The html spec defines the wbr element, which could be used because it doesn't produce a hyphen mark, it only marks a potential break point. does produce a hyphen, so it isn't helpful for Tamil.)
css-text-4 provides the hyphenate-character property, which should allow authors to indicate that Tamil should have no visible marker for hyphenation.
Tests & results:
interactive test, hyphens:auto will produce hyphenation for Tamil words
Gecko, Blink, and Webkit all fail to hyphenate the Tamil text when hyphens is set to auto.
Santhosh Thottingal has written a JavaScript-based tool for hyphenating Indian scripts, which mostly relies on syllable-breaks plus a few additional rules.
Browser bug reports:
Chromium • Webkit • Mozilla
Priority:
The impact of this is basic, because of the difficulties of handling text in narrow columns.
GitHub issue #78
Languages: ta 2
line-break:anywhere causes lines to break inside words. It should break lines on grapheme cluster boundaries for all consonant clusters apart from the 3 special conjuncts. Chrome doesn't support the anywhere value. Firefox and Safari behave as expected.
The exceptions are the sequences க்ஷ k͓ʂ, and ஶ்ரீ ʃ͓ɾī / ஸ்ரீ s͓ɾī (which are synonyms). These sequences should not be broken during line breaking. Correct line breaking of these conjunct-forming sequences are not supported by default by Unicode grapheme clusters (which split them in two), and requires the application of tailored rules.
Test: line-break:anywhere should not break shri or ksha conjuncts.
Firefox is ok for shri and for ksha without a vowel-sign, but in ரிக்ஷா leaves க் on previous line, still shaped for half a conjunct. Safari is ok for shri in HTML, but leaves ஸ் behind in textarea; for ksha, in textarea leaves க் behind, in HTML initially moves whole word to next line, then puts ரி back at end of line as you decrease the window width.
Similar results are produced for word-break: break-all, except that Chrome supports this property and value. Chrome wraps ஸ்ரீந as a single unit and ரிக்ஷா as a unit.
The impact of this is advanced, although it would be good to fix it.
GitHub issue #77
Languages: ta 2
In general, there are no issues with ordinary Tamil line-breaking. Line-break opportunities occur at the spaces between words, and characters that are not supposed to appear at a line start do not.
The exception to the latter is that । [U+0964 DEVANAGARI DANDA] and ॥ [U+0965 DEVANAGARI DOUBLE DANDA] will wrap alone to the beginning of a line if there is a space between them and the previous word. This is the case for all browsers.
Test: A line should not start with a danda character even if it is separated from the previous word by a space.
The impact of this is advanced, although it would be good to fix it.
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? Does the script indent the first line of a paragraph?
GitHub issue #80
Languages: ta 2
Tamil words can be quite long, which can cause problems for justified text, especially in narrow columns, because large gaps can appear between words, or at the end of a line if only one word fits on that line. To mitigate this, especially in the absence of hyphenation, lines that are justified in Tamil should automatically stretch words to fit in the following cases.
When only one word fits on a line, that word should be stretched to fit the whole line. Here is an example:
Where a small number of words appears on a line, the words on that line may also be stretched, so as to reduce the inter-word spacing. Here is an example:
Note that justification doesn't stretch words unless one of these cases applies.
However, a distinctive feature of Tamil is that the adjustments applied should equally expand the space between all unconnected, spacing glyphs (including the space between various vowel-signs and their base), rather than solely putting space around syllables, grapheme clusters or even code points. Here is an example:
More information:
* Approaches to full justification
* Tamil Layout Requirements
* Tamil orthography notes
Specs:
css-text provides an auto value for the text-justify property, which relies on the UA to determine the justification algorithm to follow, based on a balance between performance and adequate presentation quality, and taking into account writing system and language.
The spec says: For example, the UA could use by default a justification method that is a simple universal compromise for all writing systems—such as primarily expanding word separators and between CJK typographic letter units along with secondarily expanding between Southeast Asian typographic letter units. Then, in cases where the content language of the paragraph is known, it could choose a more language-tailored justification behavior e.g. following the Requirements for Japanese Text Layout for Japanese [JLREQ], using cursive elongation for Arabic, using inter-word for German, etc.
Tests & results:
interactive test, With CSS set to text-align:justify; text-justify:auto, when large gaps appear between justified words in Tamil the browser will automatically reduce the gaps by stretching words on the affected line.
- Gecko: ❌ *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:94.0) Gecko/20100101 Firefox/94.0*
- Blink: ❌ *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.69 Safari/537.36*
- Webkit: ❌ *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.1 Safari/605.1.15*
interactive test, With CSS set to text-align:justify; text-justify:auto, when a narrow column means that only one Tamil word fits on a line, the word will be stretched to fit the whole width of the column
- Gecko: ❌ *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:94.0) Gecko/20100101 Firefox/94.0*
- Blink: ❌ *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/95.0.4638.69 Safari/537.36*
- Webkit: ❌ *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.1 Safari/605.1.15*
interactive test, When inter-character spacing is applied to Tamil, equal space is added between all unligated spacing glyphs, including between the glyphs forming vowel-signs and their base characters, but ligated glyphs and non-spacing combining characters are not separated from the base.
- Gecko: ✅❌ Inter-character spacing is applied, but inter-glyph spacing is not. *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:96.0) Gecko/20100101 Firefox/96.0*
- Blink: ❌ No inter-character spacing is applied. *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/97.0.4692.71 Safari/537.36*
- Webkit: ❌ No inter-character spacing is applied. *Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.2 Safari/605.1.15*
Browser bug reports:
Gecko • Blink • Webkit
Priority:
The impact of this is marked as advanced, because oversized gaps in text seem to be fairly common in Tamil printed materials, but perhaps this should be basic instead? Availability of hyphenation for Tamil would also ease this issue, but that is not yet supported by browsers.
This section is concerned with spacing that is adjusted around and between characters on a line in ways other than attempts to fit text to a given width (ie. justification). 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? If spacing needs to be applied between letters and numbers, is that possible? What about space associated with punctuation, such as the gap before a colon in French? (For justification related spacing, see 7.2 Text alignment & justification.)
GitHub issue #118
Languages: hi bn ta gu pa 2
This issue applies to all languages that use letter-spacing.
Currently browsers that apply letter-spacing do so by adding a space after every letter in the text that is tracked. This results in a superfluous space at the end of the range, which creates an inappropriate gap before the following text. Letter spacing at the end of a line makes the line look misaligned in justified or right-justified text. It also has implications for text that has other styling, such as an outline or a coloured background, at the same time as being stretched.
For more details, see this GitHub issue, which is being used to track this gap. Please add any discussion there, and not to this issue.
GitHub issue #117
Languages: hi bn ta gu 2
This issue is applicable to most languages that form conjuncts from consonant clusters using an invisible virama.
A consonant cluster that uses a conjunct (rather than visible virama) should not be split when letter-spacing is applied.
Relying on grapheme clusters as the main segmentation approach fails for many Indic scripts because conjuncts are composed of multiple grapheme clusters, and should be kept together as a unit.
For these situations it is necessary to tailor the segmentation algorithm, so that it recognises the whole consonant cluster plus any attached vowel-signs or combining characters as a single unit.
For examples see Typographic character units in complex scripts.
See also notes on segmentation for the following orthographies relevant to this project: Hindi, Bangla, Punjabi, Tamil.
css-text-3 CSS uses the concept of 'typographic character unit', rather than grapheme cluster, in its specs with the explanation that the cases just described go beyond the scope of the grapheme cluster concept and that implementations should provide appropriate support. The spec doesn't provide details about the support needed for each language.
The Unicode Consortium made some attempts to address this issue, but it has so far not yielded results. CLDR now flags up a few scripts for which conjuncts are common.
Keeping conjuncts together is a pretty basic requirement. It is not possible to work around this problem.
That said, letter-spacing is not relied on for essential content authoring, therefore the priority was set to advanced.
Interactive test, When letter-spacing is applied to Devanagari the browser will not split conjuncts
Interactive test, When letter-spacing is applied to Bengali the browser will not split conjuncts
- Gecko: ❌ Most of the half-form conjuncts (which is the large majority of all conjuncts) have space inserted between the glyphs that make up the conjunct (ie. not split into consonants with visible viramas). Vertically-combined glyphs tend not to be split.
- Blink: ❌ Same as Gecko.
- Webkit: ❌ Same as Gecko.
tbd
tbd
Does the browser support requirements for baseline alignment between mixed scripts and in general? Are there issues related to line height or inter-line spacing, etc.? Are the requirements for baseline or line height in vertical text covered?
Are there list or other counter styles in use? If so, what is the format used and can that be achieved? Are the correct separators available for use after list counters? Are there other aspects related to counters and lists that need to be addressed? Are list counters handled correctly in vertical text?
GitHub issue #93
Languages: hi bn ta gu pa ks mr as mni 3
Customisable counters are needed for many languages.
Many orthographies use native digits or letters for counters, such as those used for list numbering or numbering chapter headings, etc. It needs to be possible to use these local conventions for counters.
Users also need to be able to adapt counter styles for a given context or create new ones where the browser doesn't have baked-in support. Often customisation needs are driven by the need to change the counter suffix for particular contexts, but in some cases the algorithms used for numbering can vary from author to author as well.
More:
These are just a few examples out of many.
The major browser engines support a number of hard-coded counter styles. But when this gap was first reported only Gecko supported user defined counter styling. This meant that native counters were not available for a large number of languages, and the styles could not be tweaked by the author for special uses.predefined-counter-styles contains templates for counter styles that can be applied by users if the custom counter styles spec is supported.
css-counter-styles-3 explicitly defines a number of local styles, and the other counter styles can be defined by users if the Counter Styles spec's generic mechanism for defining counter styles was implemented.
The impact of the lack of support cited here is mitigated by the tendency to use western counters, so the impact could be marked as advanced. However native styles (at least the numeric) are widely used in non-Web content, and these features are likely to be widely used when implemented across all major browsers. Therefore the priority is set to basic.I18n test suite, Predefined styles.
Contains tests for the styles that are explicitly defined in the Counter Styles spec. Gecko and Blink provide good coverage. Webkit covers most styles with some gaps, but fails for CJK and Ethiopic styles. I18n test suite, Basic custom counter styles.
The spec is essentially done, and Gecko and Blink have implemented it. No support from Webkit.
Blink • WebKit
Fixed ! Gecko, Blink, and Webkit latest browser versions now all support custom counter styles.See Can I Use?
GitHub issue #82
Languages: ta 3
Customisable counters are needed for many languages.
There is no general support for counters that use the Tamil script or digits. There is also no way for users to create their own counter styles, or to modify things such as prefix/suffix assignments for particular contexts.
This gap is now fixed. For more details, see this GitHub issue, which is being used to track this gap. Please add any discussion there, and not to this issue.
What follows are Tamil-specific notes.
For Tamil the numeric style is most common, although there is also a question about whether an alphabetic counter style needs to be defined for Tamil. An additive style is used in older texts.
Specs:
predefined-counter-styles Two Tamil counter styles are defined in this document: tamil (numeric) and ancient-tamil (additive).
css-counter-styles-3 All of these counter styles could be defined by users if the Counter Styles spec's generic mechanism for defining counter styles was implemented. The spec is essentially done. The numeric style is defined explicitly in this specification; the additive style, however, relies on the user-defined mechanism in order to be applied.
Issue, Are alphabetic counter styles common in Tamil content? Open.
Tests & results:
I18n test suite, Simple numeric.
The numeric counter style is only supported by Gecko. Blink and Webkit do not support it.
I18n test suite, Ancient-Tamil.
Neither Gecko, Blink, nor Webkit support it.
I18n test suite, Basic custom counter styles.
The spec is essentially done, but so far only Gecko has implemented it. Blink and Webkit do not support it (however, we are hopefully close seeing this feature supported in Blink, too).
Browser bug reports:
Blink
Priority:
The impact of the lack of support cited here is mediated by the tendency to use western counters, however there appears to be a desire for native styles (at least the numeric) to be made available. So the impact is being marked as advanced.
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?
GitHub issue #116
Languages: ta 2
When the start of a line contains a consonant cluster that uses a conjunct (rather than visible virama), ::first-letter should highlight the whole cluster. Usually, modern Tamil has only two of these conjuncts, however one of them can be created in two ways (making a total of 3 clusters to test).
This doesn't work well if segmentation relies on Unicode grapheme clusters, since a conjunct with two consonants will be parsed as two grapheme clusters (the first ending after the virama, and the second starting with the second consonant and including any following vowel-signs or other combining characters).
For these situations it is necessary to tailor the segmentation algorithm, so that it recognises the whole consonant cluster plus any attached vowel-signs or combining characters as a single unit. This is a particular issue for Tamil, since all other clusters are typically decomposed and show the virama.
Specs:
css-text-3 CSS uses the concept of 'typographic character unit', rather than grapheme cluster, in its specs with the explanation that the cases just described go beyond the scope of the grapheme cluster concept and that implementations should provide appropriate support. The spec doesn't provide details about the support needed for each language.
The Unicode Consortium made some attempts to address this issue, but it has so far not yielded results. CLDR now flags up a few scripts for which conjuncts are common. Tamil is not among them.
Tests & results:
Interactive test, When ::first-letter is applied to Tamil the browser will select the KSHA and SHRI conjuncts as a single unit
Gecko produces the expected result. Blink, and Webkit only select the first consonant+pulli.
Browser bug reports:
Chromium • Webkit
Priority:
The impact here is advanced, since the impact of the failures cited here on the user is likely to be very small, especially since they can resort to markup in the rare cases where the conjuncts are not properly handled. Not many words begin with the conjuncts tested. (One example of such would be ஶ்ரீநகர்)
GitHub issue #84
Languages: hi bn ta gu pa 2
Having selected the correct text for highlighting, it is important to ensure proper alignment of the baseline and height of the initial letter highlight relative to the other lines of text. This doesn't work well without help from the dedicated CSS properties, initial-letters and the initial-letters-align. Unfortunately, only Safari supports the first property, and it requires the -webkit prefix, so this is still an immature feature.
Safari aligns the alphabetic baseline of the highlighted text with that on the specified number of lines. The relationship between the highlighted letters and the first line of the paragraph appears to be based on cap height, but is not clear. The requirements for that relationship are not yet really clear, despite the information in Indian Layout Requirements.
The impact here is advanced, since it is mainly needed for advanced layouts.
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 also 8.2 Grids & tables.
As a subtopic of page layout, does the script have special requirements for character grids or for tables?
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. Are there other aspects related to user interaction that need to be addressed?