You can find the full source code for this website in the Seam package in the directory /examples/wiki. It is licensed under the LGPL.
The Java EL 2.1 specification defines an Expression Language as (a language that) makes it easy for page authors to access and manipulate application data without having to master the complexity associated with programming languages such as Java and JavaScript. In practice, the Java EL provides a shorthand way to look up JavaBeans, call getters, call setters, and call other methods.
There are other Expression Languages, but this FAQ only deals with the EL as defined by various Java JSRs.