Returns a reference to the element by its ID; the ID is a string which can be used to identify the element; it can be established using the id attribute in HTML, or from script.
The id property of the MozNDEFRecord interface is application dependent (an appropriate id can be used, depending on functionality), but generally will return an NDEF Record identifier. 
The id read-only property of the DataStoreChangeEvent interface returns the identifier of the changed record in the data store. This must return null if the operation is cleared.
The id read-only property of the DataStoreTask interface returns the identifier of the changed record in the data store. This must return null if the operation is cleared or done.