便利层 API 为每个文档特性实现一套 API，一个特性可能涉及多个 XML 元素。
The convenience layer API implements a suite of APIs for each document feature, and one feature might cover multiple XML elements.
但是，这种设计看起来与便利层的目标冲突，便利层主要关注文档特性，一个特性可能控制多个xml元素。
But this design seems to conflict with the convenience layer goal, which is to focus on the feature, where one feature might control multiple XML elements.
第三章主要对XORBAC模型的约束规范进行了集中讨论，从XORBAC模型的一般性约束和XML文档特性相关的约束两方面入手，最终为XORBAC模型总结了一套合理、全面和有效的约束规范。
It starts in terms of both general constraints and XML document-specific constraints and finally a set of reasonable, full-around and effective constraints specifications for XORBAC model is given.
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