Microsoft Typography
February 2002

This document presents information that will help font developers create or support OpenType fonts for all Arabic 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
• Appendices

Introduction

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

This document also presents information about the Arabic OpenType shaping engine of Uniscribe, the Windows component responsible for text layout.

In addition to being a primer and specification for the creation and support of Arabic 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 'lam' character is U+0644. A character may have multiple forms of glyphs.

Diacritic Marks - A character that is positioned above or below a character to provide pronunciation guidance (i.e. accent acute, grave, tilde, etc.)

Glyph - A glyph represents a form of one or more characters. For example, the final, initial and medial 'lam' glyphs (U+FEDE, U+FEDF & U+FEEO) are all forms of the 'lam' character (U+0644).

Kashida - Also known as the 'tatweel' character (U+0640). This character is used for elongation between connecting characters and is used for justification.

Ligature - A combination of glyphs that join to form a single glyph. For example, the 'lam alef' combinations of glyphs are mandatory ligatures for Arabic. Other ligatures, like 'lam meem initial', are optional.