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.

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. 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.

Sending comments on this document

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To make it easier to track comments, please raise separate issues or emails for each comment, and point to the section you are commenting on  using a URL.

Introduction

The W3C needs to make sure that the text layout and typographic 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 issues for languages using the Khmer script, including Cambodian, in terms of support by specifications or user agents (browsers, e-readers, etc.).

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

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.

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.)

Characters and phrases

Encoding considerations

Are there any character repertoire issues preventing use of this script on the Web? Do variation selectors need attention?

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.

Font styles

Do italic fonts lean in the right direction? Is synthesised italicisation problematic? See available information or check for currently needed data.

Glyph control

Does the script in question require additional 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? See available information or check for currently needed data.

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.

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.

Default quotation marks for q element

If the html tag sets the language of a page, the HTML specification says that the q element should by default produce quotation marks according to the information in CLDR for that language.

For Khmer, the default quote marks according to CLDR should be, reading right to left, “...”, and embedded quote marks ‘...’. Edge fails to produce any quotation marks, although it does so for other languages. (Firefox, Chrome & Safari are ok.) See a test and results.

Default quotation marks in a new language section

In addition, the default quotation marks for the q element are not set to the appropriate characters by the browser when the element appears inside an Khmer section of a page that has a different overall language. This is currently per the HTML specification (both W3C and WhatWG). There is an issue raised against the WhatWG version for this to be changed.

Embedded quotations in a different language

Khmer quotes embedded in text in another language can also be problematic if the outer language uses different quotation marks. This is due to the browsers choosing default quotation marks based on the language of the quotation, rather than that of the surrounding text. See a test. This behaviour is specified in the WhatWG version of the HTML spec, but no longer in the W3C version. There is an issue raised against the WhatWG version for this to be changed.

Marking all the above as advanced, because use of the q element is optional (quote characters can be used instead), and it can be styled using CSS for the general case.

Numbers, dates, etc.

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)? See available information or check for currently needed data.

Text boundaries & selection

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? Are there issues when applying punctuation than could be fixed by the application? (Some of the answers to these questions may be addressed in other sections, such as line-breaking, or initial-letter styling.) See available information or check for currently needed data.

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.

Inter-character spacing

Some scripts create emphasis or other effects by spacing out the 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.

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.

Letter-spacing

There is a test for CSS letter-spacing property.

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.

Justify, inter-character

There is a test for CSS text-justify property with value set to inter-character.

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.

Ruby annotation

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? See available information or check for currently needed data.

Text decoration

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.

Emphasis & highlights

Bold and italic are not always appropriate for expressing emphasis, and some scripts have their own unique ways of doing it, that are not in the Western tradition at all. Does this script require support for emphasising or highlighting text that cannot be achieved currently? See available information or check for currently needed data.

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.

Other inline features

Does the script have special ways of representing inline notes (such as wakiten or kumimoji in Japanese) or other inline features that need to be supported? See available information or check for currently needed data.

Lines and Paragraphs

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.

Requirements

Although Khmer doesn't use spaces or dividers between words, the expectation is that line-breaks occur at word boundaries.

There are three basic types of Khmer word:

  1. Single, indivisible words: eg. ជាតិ, វិទ្យាល័យ, កម្ម
  2. Words with prefixes and suffixes: eg. អន្តរជាតិ, មហវិទ្យាល័យ and កម្មករ
  3. Compound words (combing 2, 3, or more single words): eg. ជាតិសាសន៍, កម្មផល, សកលវិទ្យាល័យ

The first two types cannot be broken, but the third type can. For example, |ជាតិ|សាសន៍|, |កម្ម|ផល|, and |សកល|វិទ្យាល័យ. (Hong)

Text is not broken at sub-word syllable boundaries. In fact, this is particularly difficult to do algorithmically in Khmer, because syllable-final consonants are indistinguishable from consonants with an inherent vowel that constitute a new syllable. Some kind of morphological analysis is needed.

Gaps

"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.

Status

I mark this as advanced for now for the Cambodian language, although i'm 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.

Hyphenation

Is hyphenation used for your script, or something else? If hyphenation is used, does it work as expected? See available information or check for currently needed data.

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? See available information or check for currently needed data.

Counters, lists, 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 and Safari, but not by Edge.

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, I will mark the status for this as ok.

Initial letter styling

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.

Baselines & inline alignment

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

Other paragraph features

In your script, is the first line of text typically indented at the start of a paragraph? Are there other features of paragraph design that are peculiar to your script? See available information or check for currently needed data.

Layout & pages

Bidirectional layout

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. See available information or check for currently needed data.

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.

Notes, footnotes, etc.

Does your script have special requirements for notes, footnotes, endnotes or other necessary annotations of this kind in the way needed for your culture? See available information or check for currently needed data.

Page numbering, running headers, 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.

Other page layout & pagination features

Some cultures define page areas and page progression direction very differently from those in the West (eg. kihon hanmen in Japanese). Is this an issue for you? Are widows and orphans relevant? In what order do pages progress, RTL or LTR? See available information or check for currently needed data.

Other

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).

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

Acknowledgements

Special thanks to the following people who contributed to this document (contributors' names listed in in alphabetic order).

This Person, That Person, etc

Please find the latest info of the contributors at the GitHub contributors list.