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 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.
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 Southeast Asian Language Enablement (sealreq), 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.
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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 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.
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.
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.)
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 3.3 Letterform slopes, weights, & italics.
GitHub issue #75
Languages: km 2
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:
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.
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.
Interactive test, font-family:generic(mul) will apply a Mul font in Khmer
Discussion document: Generic font families
CSS discussion threads:
The CSS Fonts 4 spec now defines a generic(ident) syntax which will be used for newly-introduced, and especially for script-specific, generics.
The CSS WG resolved to add this as a new generic font family, and generic(khmer-mul) is now in CSS Fonts 4-def).
Browsers are not yet supporting it.
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 3.4 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 6.1 Line breaking & hyphenation, or 6.6 Styling initials.)
GitHub issue #35
Languages: km 2
"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:
- Bad and ambiguous spellings are correctly handled
- 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:
- disable the dictionary lookup and let the line-breaking depend on ZWSP insertion, or
- 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.
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 5.2 Quotations & citations, and 5.4 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 7.3 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?
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 #35
Languages: km 2
"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:
- Bad and ambiguous spellings are correctly handled
- 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:
- disable the dictionary lookup and let the line-breaking depend on ZWSP insertion, or
- 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.
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?
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 6.2 Text alignment & justification.)
GitHub issue #36
Languages: km 2
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.
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?
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?
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 7.2 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?