I have looked up the prerelease of the chapter on Manuscript
Description for P5 (at http://www.tei-c.org/Activities/MS/FASC-
ms.pdf), and in 1.2.3 "References to manuacript locations",
Example 1.10 indicates that the element 'locus' should be available
in the elements 'p', put when I am testing this with P5, it looks like
that is not the case. Is the error in the chapter or in the P5?