@Retention(value=RUNTIME)
@Target(value=PARAMETER)
@Documented
public @interface JsOptional
Note that JsOptional can only be used in a JsConstructor, a JsMethod or a JsFunction method. An optional argument cannot precede a non-optional argument (a vararg is considered an optional argument).
This annotation is informational in the GWT compiler but other compilers or tools might use it for example to annotate types in the output JavaScript program.