Some years ago we had this ticket:
which was supposed to result in the removal of "mandatory when applicable" wherever it occurred, on the basis that it's pretty much meaningless. However, it still appears in attDef/@usage:
where it remains meaningless, along with its shady partner "recommended when applicable".
Something is either mandatory or it's not. Similarly, it's silly to say that something is recommended when applicable; how could it be recommended when it's not applicable, and how could rwa be different from simply "recommended", which also exists?
I recommend (if applicable) removing mwa and rwa from this list.