Khmer Gap Analysis

W3C Group Draft Note

More details about this document
This version:
https://www.w3.org/TR/2024/DNOTE-khmr-gap-20240314/
Latest published version:
https://www.w3.org/TR/khmr-gap/
Latest editor's draft:
https://w3c.github.io/sealreq/gap-analysis/khmr-gap
History:
https://www.w3.org/standards/history/khmr-gap/
Commit history
Editor:
(W3C)
Feedback:
GitHub w3c/sealreq (pull requests, new issue, open issues)

Abstract

This document describes and prioritises gaps for the support of Khmer 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. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This document describes and prioritises gaps for the support of languages using the Khmer 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. This document complements the document Khmer Layout Requirements, 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 Southeast Asian 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 Group Draft Note using the Note track.

Group Draft Notes are not endorsed by W3C nor its Members.

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.

The W3C Patent Policy does not carry any licensing requirements or commitments on this document.

This document is governed by the 03 November 2023 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 Cambodian language in the Khmer 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.

For a description of the Khmer script see the (non-W3C) page Khmer, which summarises aspects of the orthography and typographic features, including relevant Unicode characters and their use.

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, Khmer Layout Requirements. 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.

Key:

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.

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.

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.

#75 Font fallback should allow selection of a Mul font

This issue is applicable to Khmer script orthographies.

Modern Khmer has several distinct styles of font, each of which is used for different purposes. The round style (អក្សរមូល /ʔɑːksɑː muːl/) has heavier, more rounded letter shapes, and includes more ligated forms. It is commonly used for titles and headings in Cambodian documents, books, or currency, as well as on shop signs or banners. It may also be used to emphasise important names or nouns. The regular font weight looks like bolded text in comparison to the upright font style.

Authors using a Mul font in their text should be able to indicate that any font fallback picks a Mul font, rather than a random Khmer font. Otherwise, the distinctions between certain types of text on a page may be lost.

More:

The GAP
Currently there is no way to tell the browser to fall back to a Mul font, rather than another font.

Neither Gecko, Blink, nor Webkit support this. Before they can, CSS needs to provide a way for authors to indicate that a khmer mul generic font should be used.

Priority
This is a useful feature for Khmer, which uses the Mul style frequently in documents and signage. Marking as Advanced, since there is not the imperative to use such a font (unlike some other font styles). Some may see this as Basic, given the prevalence of this convention.

Tests & results
Interactive test, font-family:generic(mul) will apply a Mul font in Khmer

Action taken
Discussion document: Generic font families

CSS discussion threads:

Outcomes
The CSS Fonts 4 spec now defines a generic(ident) syntax which will be used for newly-introduced, and especially for script-specific, generics.

generic(mul) has not yet been added as one of the generic family names.

Browsers are not yet supporting it.

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.

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.

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.

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.

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.

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.

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.

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.

#35 Using dictionaries can create problems for word-breaking

"ICU use word boundaries to break but it looks not nice, because it depend on the people who provide wordlist, for example the name of USA (United State of America) in Khmer it is សហរដ្ឋអាមេរិក ICU consider as one word, when it break to new line, it remain the long blank in old line. Normally, we can break it to 2 word សហរដ្ឋ = United State and អាមេរិក." (Hong)

"There is a change going through ICU at the moment, to how Khmer is line broken. The basis of line breaking is still dictionary based and word broken. There is no intent to support syllable breaking. The following changes are made in that change:

  1. Bad and ambiguous spellings are correctly handled
  2. Use of ZWSP and WJ are disambiguated with regard to how far they limit linebreaking. In the case of Khmer they have a range of up to 3 small clusters (base+Marks+Coengs) but may collapse to 0 for longer words." (@mhosken)

An issue with the use of dictionary lookup is that browsers don't have dictionary lookup support for minority languages that use the Khmer script. And in fact, regardless of the declared language of the text, browsers tend to apply the Khmer dictionary to text written in the Khmer characters.

For such languages, it would be helpful if the content author could either:

  1. disable the dictionary lookup and let the line-breaking depend on ZWSP insertion, or
  2. invoke a different dictionary – perhaps one that is provided as a browser extension.

Marking this as advanced for now for the Cambodian language, but open to arguments that the difficulties produced are worth a status of basic.

For minority languages, the status is clearly going to be broken, since there's no way to override the use of the Khmer dictionary.

See also hyphenation below.

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.

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.

Firefox on MacOS keeps all vowel signs and diacritics with base characters. It also keeps together consonant stacks and their vowel signs, such as ខ្លួ. Also, ligated combinations such as បា កា are rendered as expected.

Chrome and Safari don't support text-justify: inter-character.

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.

#36 Letter-spacing breaks text units

Cambodian text doesn't appear to use inter-letter spacing in running text, however it is sometimes used in signage. (@mcdurdin) See an example. The rules for where the separations appear are still not clear, however one might expect that it keeps together base + subjoined consonants, and base consonants + vowel signs. The situation is less clear for spacing vowel-signs such as ◌ា [U+17B6 KHMER VOWEL SIGN AA​], which are shown separated in the example linked to above.

Firefox on MacOS keeps all vowel signs and diacritics with base characters. It also keeps together consonant stacks and their vowel signs, such as ខ្លួ. Also, ligated combinations such as បា កា are rendered as expected.

Chrome on MacOS fails to keep vowel signs together with a preceding subjoined consonant.

Safari separates all characters, combining or not.

I'm marking this as advanced, even though it's broken on Chrome and Safari, until someone proposes that it really is needed for Web or eBook content. Happy to change.

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.

Two numeric CSS counter styles are defined for Khmer, using Khmer digits, in the document Ready-made Counter Styles: khmer and cambodian. Both styles are exactly the same, and are listed separately because both names are supported in some browsers, and it makes it easier to cut and paste if two clean instances are provided.

In addition, an alphabetic counter style is defined: khmer-consonant.

The CSS Counter Styles specification only specifies the khmer and cambodian styles.

The khmer and khmer counter styles are supported by Firefox, Chrome, Edge, and Safari, but not by legacyEdge.

The khmer-consonant style is not supported by any browser natively, and although the CSS Counter Styles spec allows users to create their own counter styles, the feature is only implemented by Firefox at the moment, so no support is available for this style.

See tests: Simple numericKhmer script

Unless a proposal is made that the khmer-consonant or some other style is important, marking the status for this as ok.

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.

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?

Show summary