When applying multiple composer classes separated by comma (eg. <div apply="org.zkoss.bind.BindComposer, my.own.Composer">), the ZUL editor shows an error:

Multiple annotations found at this line:

• Syntax error on token ",", . expected
• org.zkoss.bind.BindComposer.my cannot be resolved
  to a type

although such construction is legal: http://books.zkoss.org/wiki/ZK_Developer%27s_Reference/MVC/Controller/Composer#Applying_Multiple_Composers