Lao 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 Lao 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 Lao 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 Lao 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 Lao script. The information here is developed in conjunction with a document that summarises gaps where the Web fails to adequately support the Lao 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): Anousak Anthony Souphavanh, Arthit Suriyawongkul, Ben Mitchell, James Clarke, John Durdin, Martin Hosken, and Norbert Lindenberg as members of the W3C's Southeast Asian Language Enablement community.

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

1.2 About this document

This document points to resources for Lao 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 Lao script. They include requirements, tests, GitHub discussions, type samples, and more,

The document focuses on typographic layout issues. For a deeper understanding of the Lao 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, Lao Gap Analysis, which describes gaps in language support for users of the Lao 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 Lao 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 Lao 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 Lao script. See a list of unresolved questions for Lao experts. Each section below points to related discussions. See also the repository home page.

2. Lao Script Overview

The Lao orthography is an alphabet. This means that both consonants and vowels are indicated.

Lao text runs left to right in horizontal lines. Spaces separate phrases, rather than words. There is no case distinction.

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, except for one subjoined consonant, used in combination only with HA.

Syllable-initial clusters and syllable-final consonant sounds are all written with ordinary consonant letters. However, because all vowels are written, it is not difficult to algorithmically detect syllable boundaries.

Unlike its close relative, Thai, the Lao orthography is an alphabet and has no inherent vowel, but it still represents vowels using vowel signs (including combining marks, dedicated vowel letters, and a couple of repurposed consonants).

Vowels in Lao are written with a mixture of combining characters and ordinary spacing characters. Lao uses visual placement: only the vowel components that appear above or below the consonant are combining marks; the others are ordinary spacing characters that are typed in the order seen. There are pre-base vowel glyphs. In principle, there are no single-character circumgraphs in Lao text, but a single vowel or diphthong is frequently made up of multiple components.

There are no independent vowels, and standalone vowel sounds are written using vowel signs applied to U+0EAD LETTER O.

Lao 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.

Vowels are often written differently when they appear in a closed vs. open syllable.

Lao has native digits, and they are commonly used.

3. All topics

4. Text direction

Lao 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

8.3 Text spacing

8.4 Baselines, line height, etc.

8.5 Lists, counters, etc.

8.6 Styling initials

9. Page & book layout