Thai Script Resources

W3C Group Draft Note

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Richard Ishida (W3C)
GitHub w3c/sealreq (pull requests, new issue, open issues)


This document points to resources for the layout and presentation of text in languages that use the Thai script. The target audience includes developers of Web standards and technologies, such as HTML, CSS, Mobile Web, Digital Publications, and Unicode, as well as implementers of web browsers, ebook readers, and other applications that need to render Thai text.

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

This document points to resources for Thai script layout and text support on the Web and in eBooks. These requirements provide information for Web technologies such as CSS, HTML and digital publications about how to support languages written using the Thai script. The information here is developed in conjunction with a document that summarises gaps where the Web fails to adequately support the Thai script.

The editor's draft of this document is being developed in the GitHub repository Southeast Asian (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.

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.

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.

Some links on this page point to repositories or pages to which information will be added over time. Initially, the link may produce no results, but as issues, tests, etc. are created they will show up.

Links that have a gray color led to no content the last time this document was updated. They are still live, however, since relevant content could be added at any time. When the document is updated, links that now point to results will have their live colour restored.

1. Introduction

1.1 Contributors

This document was created by Richard Ishida.

The following people contributed information that was used in preparing this document (in alphabetic order): Ben Mitchell, Danh Hong, Marc Durdin, and Martin Hosken as members of the W3C's Southeast Asia Language Enablement community.

See also the GitHub contributors list for the Southeast Asian Language Enablement project, and the discussions related to the Thai script.

1.2 About this document

This document points to resources for Thai script layout and text support on the Web and in eBooks. These resources provide information for developers of Web technologies such as CSS, HTML and digital publications, and for application developers, about how to support languages written using the Thai script. They include requirements, tests, GitHub discussions, type samples, and more,

The document focuses on typographic layout issues. For a deeper understanding of the Thai script and how it works see Southeast Asian Orthography Notes, which includes topics such as: Phonology, Vowels, Consonants, Encoding choices, and Numbers.

1.3 Gap analysis

This document should be used alongside a separate document, Thai Gap Analysis, which describes gaps in language support for users of the Thai script, and prioritises and describes the impact of those gaps on the user.

Gap reports are brought to the attention of spec and browser implementers, and are tracked via the Gap Analysis Pipeline. (Filter for Thai script items)

The document Language enablement index points to this document and others, and provides a central location for developers and implementers to find information related to various scripts.

The W3C also has a repository with discussion threads related to the Thai script, including requests from developers to the user community for information about how scripts/languages work, and a notification system that tracks issues in W3C working groups related to the Thai script. See a list of unresolved questions for Thai experts. Each section below points to related discussions. See also the repository home page.

2. Thai Script Overview

The Thai orthography is an abugida. Consonant letters have an inherent vowel sound. Vowel signs are attached to the consonant to produce a different vowel.

Thai text runs left to right in horizontal lines.

Spaces separate phrases, rather than words.

Each onset consonant is associated with a high, mid, or low class related to tone. Tone is indicated by a combination of the consonant class, the syllable type (live/dead), plus any tone mark.

No conjuncts are used for consonant clusters.

Syllable-initial clusters and syllable-final consonant sounds are all written with ordinary consonant letters. It can therefore be difficult to algorithmically detect syllable boundaries.

An inherent vowel is pronounced o inside a closed syllable, a in an open syllable, and ɔː before a final -r. Non-inherent vowels are represented using vowel signs. Characters used to represent vowels and dipthongs include combining marks, vowel letters, and consonants. There are pre-base vowel glyphs, but Thai uses visual placement: only the vowel sign components that appear above or below the consonant are combining marks; the others are ordinary, spacing letters that are typed in the order seen.

There are no independent vowels, and standalone vowel sounds are written using vowel signs applied to U+0E2D THAI CHARACTER O ANG.

Thai has a large number of multipart vowels (including diphthongs) made from dedicated vowel characters and from consonants. Composite vowels can involve up to 4 glyphs (plus a tone mark), and glyphs can surround the base consonant(s) on up to 3 sides, eg. เกี๊ยะ kía̯ʔ geta (footwear)

Thai has vocalics.

Thai has native digits, and they are commonly used.

3. All topics

4. Text direction

Thai is written horizontally, left to right.

5. Glyph shaping & positioning

5.1 Fonts & font styles

5.2 Context-based shaping & positioning

5.3 Letterform slopes, weights, & italics

6. Typographic units

6.1 Characters & encoding

6.2 Grapheme/word segmentation & selection

7. Punctuation & inline features

7.1 Phrase & section boundaries

7.2 Quotations & citations

7.3 Emphasis & highlighting

7.4 Abbreviation, ellipsis & repetition

7.5 Inline notes & annotations

7.6 Text decoration & other inline features

8. Line & paragraph layout

8.1 Line breaking & hyphenation

8.2 Text alignment & justification

Justification in Thai adjusts the space between phrases, but also makes certain adjustments to inter-character spacing.

8.3 Text spacing

8.4 Baselines, line height, etc.

8.5 Lists, counters, etc.

8.6 Styling initials

9. Page & book layout