In order for a web server to provide optimised content to different client devices it requires a description of the capabilities of the client known as the delivery context. In previous work we demonstrated DELI, an open-source library that allows Java servlets to resolve HTTP requests containing delivery context information in CC/PP or UAProf formats. Subsequently DELI has been incorporated into the Apache Cocoon XML publishing framework in order to demonstrate how delivery context information can be used in conjunction with content transformation via XSLT. During this work, it was found that it is cumbersome to match this information using constraints written in XPath. Furthermore there is no easy method of abstraction so that common sets of constraints may be reused in multiple stylesheets. This report describes an alternative mechanism for delivery context matching called capability classes (patent pending). This report outlines how to implement capability classes and how they may be applied to various content specialisation techniques such as content transformation, negotiation or generation. It also compares and contrasts capability classes with device classes and media queries. 11 Pages