item - FormItem, DataSourceField or ListGridField on which this validator was
declared. NOTE: FormItem will not be available during a save performed without
a form (eg programmatic save) or if the field
is not available in the form.
additionalContext - Object containing extra context which may be useful to the condition function.
Contains the following properties: component: the DynamicForm or ListGrid being validated
rowNum: the row number of the cell being validated (only if component is a ListGrid) colNum: the
column number of the cell being validated (only if component is a ListGrid)
whether the value passed validation. True for passed, false for fail.