And another:
26) Section 2.4 specifies how PUT is used to update an annotation.
The example shows the replacement annotation RDF having a subject
URI; i.e.
<r:Description
r:about="
http://annotea.example.org/Annotation/3ACF6D754">
...
The spec does not say if the subject URI is mandatory. It also
does not state that the URI (if present) needs to match the
URI in the request. The same comment applies to Section 3.4.