EnclosedExpr in constructors

For constructors, the introductory text now introduces enclosed expressions and content expressions:

<quote>
Constructors are provided for element, attribute, document, text, comment, and processing instruction nodes. Two kinds of constructors are provided: direct constructors, which use an XML-like notation that can incorporate enclosed expressions, and computed constructors, which use a notation based on enclosed expressions. [Definition: An enclosed expression is an instance of the EnclosedExpr production, which allows an optional expression within curly braces.] [Definition: In an enclosed expression, the optional expression enclosed in curly braces is called the content expression.] If the content expression is omitted, the value of the content expression is ().
</quote>

Up to now, content expressions only lived in node constructors, but it would be handy to simply use these definitions in other places where EnclosedExpr can occur, otherwise managing the vocabulary is a little more fiddly.  Would this be a reasonable thing to do?

Jonathan