In 12.1.2 Readings, we find the following:
The hand and resp attributes are intelligible only on an element recording a reading from a single witness, and should not be used if more than one witness is given on the same rdg or lem element. If more than one witness is given for the reading, they are undefined. To convey this information when the witness is one among several, the witDetail element should be used;
But witDetail can't take @hand, because it is not a member of att.textCritical. Seems like it should be...