US Patent 7437666 Expression grouping and evaluation

An apparatus comprises a stylesheet compiler and a document processor. The stylesheet compiler is configured to identify expressions in a stylesheet and is configured to generate one or more expression trees representing the expressions. Expressions having one or more common nodes are represented as children of a subtree that represents the common nodes. Coupled to receive a document and the expression tree, the document processor is configured to evaluate the expressions represented in the one or more expression trees against the document.