Microsoft Typography
April 2002

This document presents information that will help font developers create or support OpenType fonts for Lao script languages covered by the Unicode Standard.

This is a multi-page specification. To access specific pages, use the Contents section below, or the navigation bar at the bottom of each page.

Contents

• Introduction
• Shaping Engine
• Features
• Appendix

Introduction

Font developers will learn how to encode script features in their fonts, choose character sets, organize font information, and use existing tools to produce Lao script fonts. Registered features of Lao scripts are defined and illustrated, encodings are listed, and templates are included for compiling layout tables for OpenType fonts.

This document also presents information about the Lao OpenType shaping engine of Uniscribe, an operating system component responsible for text layout.

In addition to being a primer and specification for the creation and support of Lao script fonts, this document is intended to more broadly illustrate the OpenType Layout architecture, feature schemes, and operating system support for shaping and positioning text.

Glossary

The following terms are useful for understanding the layout features and script rules discussed in this document.

Base Glyph - Any glyph that can have a diacritic mark above or below it. Layout operations are defined in terms of a base glyph, not a base character, as a ligature may act as the base.

Character - Each character represents a Unicode character code point. For example, the 'ko' character is U+0E81.

Glyph - A glyph represents the displayed form of one or more characters.

Combining Mark - A vowel sign or tone mark positioned above or below a character to provide pronunciation guidance.

Cluster - The effective "unit" of Lao writing systems, consisting of a consonant, vowel signs and combining tone marks, or independent vowel letters.