<docauthor> isn't exactly metadata, it's an element of an ncx file. Look here:
NCX specification as used in EPUB idpf specification document
Wiki description of ncx elements, includes <docauthor>
Anyway, I've found my answer
here. It seems the answer is
Code:
<docAuthor>
<text>Jane Doe</text>
</docAuthor>
<docAuthor>
<text>John Smith</text>
</docAuthor>
Of course, whether the current range of reader use it is another question alltogether
