[Name] srcexpr [Required] false [Attribute Constraints] Must not occur with the 'src' attribute or the element. [Type] Value expression [Default Value] None [Valid Values] Any expression evaluating to a valid URI. [Description] 
A dynamic alternative to 'src'. If this attribute is present, the SCXML Processor MUST evaluate it when the parent element is evaluated and treat the result as if it had been entered as the value of 'src'.