BIRT Aggregate Functions

BIRT provides a number of aggregation functions, such as Total.sum() that can be called from within Javascript expressions.  But be aware that these so-called "functions" are actually macros, and are expanded by BIRT prior to execution by the Javascript engine.  The means that they can only appear at the top level of a BIRT data field expression and similar contexts.  They cannot be used in normal Javascript functions or any other non-top-level context.