This document points browser implementers and specification developers to information about how to support typographic features of scripts or writing systems from around the world, and also points to relevant information in specifications, to tests, and to useful articles and papers. It is not exhaustive, and will be added to from time to time.
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The information in this document helps to link users and developers so that browsers can better support typographic needs around the world. It is expected that this document will be constantly updated, as new material becomes available or comes to our attention.
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The W3C and browser implementers need 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 users expect.
To that end experts in various parts of the world are documenting layout and typographic requirements, as well as gaps between what is needed and what is currently supported in browsers and ebook readers. (See a list of relevant work in this area that is supported by the W3C Internationalization groups.)
This page points browser implementers and specification developers to information about how to support features of scripts or writing systems from around the world, and also points to relevant information in specifications, to tests, and to useful articles and papers. It is not exhaustive, and will be added to from time to time.
The Issues links point to ongoing discussions of two types:
Additional information and references are hereby solicited; please suggest additions, clarifications, corrections, and other improvements using the github issues list.
Many scripts use native punctuation marks in addition to or instead of those used in Latin script text. In other cases, such as Greek, common Latin punctuation marks may mean something different from what they mean in English. It may be important to understand what needs to be supported, how these punctuation marks function, and how they interact with other operations applied to the text.
See also 2.2 Quotations and 3.1 Line breaking.
Quotation marks vary from language to language, not just from script to script. Also, you should expect variations in behavior when quotation marks are nested. Furthermore, the quotation marks used for vertical Japanese text are not the same as those typically used for the same text when horizontally laid out.
See also 2.1 Punctuation.
A browser or application needs to correctly apply functions to the basic units of text, be they characters, character sequences, syllables, or words. Some scripts, such as those used in South and South-East Asia, require clusters of characters to be treated as a single unit for most editing operations. Many other scripts use combining characters such as accents, vowel signs, length markers, etc. that must be kept with the base character they are associated with.
When a user double-clicks on some text, the appropriate units should be selected. In scripts such as Chinese and Thai, 'words' should be selected even though they are not separated by spaces. In scripts such as Tibetan and Ethiopic, the word separator may be a visible character, rather than a space. It is important to understand how they should be treated when a 'word' is highlighted, or when text wraps, etc.
In some scripts, such as Arabic, it may be desirable to allow the content author to control the placement of glyphs such as diacritics, or to control ligation, etc.
Conversion between lower, upper and title case only applies to a few scripts, most scripts are unicameral. Where it does apply, the rules can vary by language.
In other cases, a particular script may require a different type of transform. For example, in Japanese it is important to be able to convert between half-width and full-width presentation forms.
Many scripts create emphasis or other effects by spacing out the letters or syllables in a word. There are questions about how this should work in Indic and SE Asian scripts, and in Arabic-based scripts which join up adjacent letters. Another aspect of inline-spacing relates to separation of characters or items in text. For example, French uses spaces before certain punctuation marks, and the traditional Mongolian script requires special spacing between word stems and certain suffixes.
Ruby is used for phonetic and semantic annotations of East Asian text, including furigana, pinyin and zhuyin fuhao systems. In addition to positioning annotations along the correct side of the base text, there are many fine adjustments of the annotation and base text to support.
Some aspects related to the drawing of lines alongside or through text involve local typographic considerations. For example, underlines need to be broken in special ways for some scripts, and the height of underlines, strike-through and overlines may vary depending on the script. For vertical text the placement needs to be to the right or left of the line of text, rather than under or over.
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 the browser or ereader correctly handle special styling of the initial letter of a line or paragraph, such as for drop caps?
Some scripts require special handling with regard to how font properties are specified and how font resources are loaded dynamically.
There are some specific rules about how scripts such as Chinese, Japanese and Korean behave when a line is wrapped. For example, these scripts tend to break a line in the middle of a word (with no hyphenation) – even in Korean, which has spaces between words.
It is common for certain characters to be forbidden at the start or end of a line, but which characters these are, and what rules are applied when depends on the script or language. In some cases, such as Japanese, there may be different rules according to the type of content or the user's preference.
Some scripts don't use hyphenation, those that do have particular rules about how it should be applied that are typically language-specific.
Typographers have come up with various methods for effective full justification – causing the text to completely fill the line, in order to create visual alignment on both edges of a paragraph.
Typographic conventions for full text justification depend on the writing system, the content language, and the calligraphic style of the text. Results also tend to vary based on the capabilities of the layout engine and a given typographer’s preferences for weighing its various detrimental effects on typographic color and readability.
The CSS specification describes a set of simple and complex styles for counters to be used in list numbering, chapter heading numbering, etc. It also provides a generic mechanism for content authors to create their own counter styles. One has to consider not only the characters and algorithms to be used (numeric, alphabetic, additive, etc), but also what the separator or other associated marks look like.
Scripts whose characters are typically written right-to-left, like Arabic, Hebrew, Thaana, and so on, become bidirectional when they include numbers or text from other scripts (such as Latin acronyms). Browsers and applications need to support bidirectionality. This means supporting the Unicode Bidirectional Algorithm, but also different visual locations of line start and end, isolation of embedded strings, correct line alignment, and so forth.
Browsers and applications must accurately and comprehensively cover requirements for baseline alignment between mixed scripts. For example, Arabic script descenders go far below those of the Latin script, and Armenian characters need to be aligned with ideographic characters in Chinese appropriately with regard to comparative heights and baselines. European, Far Eastern and South Asian scripts tend to use different baselines, which must be aligned correctly.
Some scripts have particular rules about indenting text at the start of a paragraph, or indeed whether that's normal. Some allow punctuation to hang outside the text box at the start or end of a line. There may be other aspects of how paragraphs are presented that vary from script to script, or need to be controlled by the content author.
There are special requirements for vertically oriented text. For example, it's common for content authors to want to mix short horizontal runs of text, such as 2-digit numbers, in a vertical column (tate chu yoko). It's also important to provide appropriate support for text in scripts that are normally only horizontal.
Support for notes, footnotes, endnotes or other necessary annotations of this kind may vary in other cultures. In some cases, a script may use a very idiosyncratic approach to represent notes inline or to link to footnotes.
These links point to conventions for managing the content that appears outside the main text block, for example page numbering, or the way that running headers and the like are handled.
Some cultures define page areas and page progression direction very differently from those in the West. For example, the size of the Japanese kihon-hanmen, or main text block, is traditionally established by counting character cells, and margin space is then defined by the remaining space. In right-to-left scripts, pages also progress from right to left.
This is the first public working draft.
See the github commit log for more details.