In his blog post Marcos discusses the use of expression languages within ZK, you can read the post in both English and Portuguese.
You can read his post by following the links
Marcos de Sousa works in the area of analysis, design and development of systems at BCI Bank. He is an experienced programmer using core iSeries RPG/ILE and front-end ZK supported by other frameworks like Spring, Hibernate and Quartz, while develop business analysis tools for Bank Applications. Marcos is a member of ZK Blog Network and is not an employee of Potix.
Excellent site, keep up the good work