Attributes

An attribute is a named wrapper for arbitrary data that you want to associate with another object. Whenever you query the name of a document, or set the font size of a range of text, you are using attributes. The Taligent Application Environment provides a generic attribute service for application and system programmers that allows you to create instances of existing attribute classes, or derive new ones, to suit your particular needs.

Within the Taligent Application Environment, the text subsystem is the primary client of attributes. It makes extensive use of attributes to maintain style information such as point size, font, style, and color. The Document framework also uses the attribute subsystem to provide documents with attributes. See also "Attribute concepts" in the "Text and native language support overview" chapter of Text, Native Language Support, and Time Media.

The services provided by the attribute classes include creating and tracking specific attributes, sharing attribute data among several attributes, grouping attributes and managing these groups, and relating attribute groups in a hierarchy to allow for dynamic inheritance of attributes from other groups.

After reading this chapter, you will understand how to:

Use existing attribute classes
Derive your own attributes and attribute groups
Share attributes and attribute groups to reduce storage overhead
Manage group hierarchies to get dynamic attribute inheritance

Attribute concepts
Attribute classes
Attribute group classes
Design considerations
Creating and using attributes
Defining new attribute classes

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