Test K2-DirectConElemNamespace-17 and -18 expect XQST0022, and specifically comment that bracket-escapes are invalid in namespace declarations.  In the XQuery spec, 3.7.1.2 Namespace Declaration Attributes we find:

"The value of a namespace declaration attribute must be a URILiteral; otherwise a static error is raised [err:XQST0022]."

I'd argue that the value of this attribute is "content{" which is a URILiteral since it matches:

[140]    	URILiteral 	   ::=    	StringLiteral
[144]    	StringLiteral 	   ::=    	('"' (PredefinedEntityRef | CharRef | EscapeQuot | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | EscapeApos | [^'&])* "'")

Where does the specification state that bracket-escapes are invalid in this context?

(:*******************************************************:)
(: Test: K2-DirectConElemNamespace-17                    :)
(: Written by: Frans Englich                             :)
(: Date: 2007-10-02T13:04:11+01:00                       :)
(: Purpose: A namespace must be a literal, for which bracket-escapes are invalid
. :)
(:*******************************************************:)
<e xmlns="content{{"/>

XQST0022