nsCStringKey key(prop); if (!Exists(&key)) return NS_ERROR_FAILURE;  nsISupports* prevValue = (nsISupports*)Remove(&key); NS_IF_RELEASE(prevValue); return NS_OK;
return NS_ERROR_NOT_IMPLEMENTED;
nsProperties::UndefineProperty(const char* prop){    nsCStringKey key(prop);    if (!Exists(&key))        return NS_ERROR_FAILURE;    nsISupports* prevValue = (nsISupports*)Remove(&key);    NS_IF_RELEASE(prevValue);    return NS_OK;}