There are a number of problems with updating XML documents in an XML store. The primary problem is that XQuery 1.0 does not have a facility for updating documents. The XQuery Update Facility Requirements exists but it clearly states "the WG does not intend to produce a Recommendation from this Working Draft" which leaves me with a big fat question mark over my head. This has caused each XML DB vendor to provide their own update mechanism. And this leads to the topic of this post:

BDBXML is a decent XML DB but it's somewhat rough around the edges. When updating documents it is common to get the following error:

Cannot perform a modification on an XmlValue that isn't either Node or Document type, errcode = INVALID_VALUE

To make a long story short, you cannot specify a doc('...') in the XmlQueryExpression that you specify to any of the XmlModify modification methods. The documentation implies this but does not drive the point home. Given that all non-modification uses of XmlQueryExpression require some sort of "navigation function" (collection('...'), doc('...'), etc) it feels odd not to specify it for modfications.