Eclipse Platform
Luna (4.4)

Package org.eclipse.equinox.bidi

This package provides classes for processing bidirectional text with a special structure to ensure its proper presentation.

See: Description

Package org.eclipse.equinox.bidi Description

This package provides classes for processing bidirectional text with a special structure to ensure its proper presentation.

There are various types of structured text. Each type should be handled by a specific type handler. A number of standard type handlers are supplied with this package.

Introduction to Structured Text

Bidirectional text offers interesting challenges to presentation systems. For plain text, the Unicode Bidirectional Algorithm (UBA) generally specifies satisfactorily how to reorder bidirectional text for display. This algorithm is implemented in many presentation and operating systems, like Java/Swing, Windows, Linux.

However, all bidirectional text is not necessarily plain text. There are also instances of text structured to follow a given syntax, which should be reflected in the display order. The general algorithm, which has no awareness of these special cases, often gives incorrect results when displaying such structured text.

The general idea in handling structured text in this package is to add directional formatting characters at proper locations in the text to supplement the standard algorithm, so that the final result is correctly displayed using the UBA.

A class which handles structured text is thus essentially a transformation engine which receives text without directional formatting characters as input and produces as output the same text with added directional formatting characters, hopefully in the minimum quantity which is sufficient to ensure correct display, considering the type of structured text involved.

In this package, text without directional formatting characters is called lean text while the text with added directional formatting characters is called full text.

The class StructuredTextProcessor is the main tool for processing structured text. It facilitates handling several types of structured text, each type being handled by a specific type handler :

For each of these types, an identifier is defined in StructuredTextTypeHandlerFactory :

These identifiers can be used as argument in some methods of StructuredTextProcessor to specify the type of handler to apply.

The classes included in this package are intended for users who need to process structured text in the most straightforward manner, when the following conditions are satisfied:

When their needs go beyond the conditions above, users can use classes in the org.eclipse.equinox.bidi.advanced package.

Developers who want to develop new handlers to support types of structured text not currently supported can use components of the package org.eclipse.equinox.bidi.custom. The source code of packages org.eclipse.equinox.bidi.* can serve as example of how to develop processors for currently unsupported types of structured text.

However, users wishing to process the currently supported types of structured text typically don't need to deal with the org.eclipse.equinox.bidi.custom package.

Abbreviations used in the documentation of this package

Unicode Bidirectional Algorithm
Graphical User Interface
User Interface
Left to Right
Right to Left
Left-to-Right Mark
Right-to-Left Mark
Left-to-Right Embedding
Right-to-Left Embedding
Pop Directional Formatting


Known Limitations

The proposed solution is making extensive usage of LRM, RLM, LRE, RLE and PDF directional controls which are invisible but affect the way bidi text is displayed. The following related key points merit special attention:

Eclipse Platform
Luna (4.4)

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