In order to meet the requirements of wireless device and wireless network, a wireless profile should be added to extend the CSS subset. From our point of view, the requirements of the WML-NG CSS subset should be defined as following. Processing model CSS2 processing model is based on the document tree. Creating a document tree consumes with much amount of memory, but the wireless device has not enough memory. We must realize how the memory and CPU power constraints affect the CSS processing model.
Simplicity is very important to the popularization of wireless content business.
In the WML-NG CSS subset specification, the syntax and data types should be specified simply as well as possible. These patterns, called selectors, may range from simple element names to rich contextual patterns. For the less memory and less powerful CPUs of wireless device, some selectors definition should be excluded from the CSS2. In the CSS2 specification, the import rule allows users to import style rules from other style sheets, it is very convenient to reuse the other style sheet resources. But for the less powerful CPUs of wireless device and less bandwidth of wireless network, processing the import rule would be heavy.