why must one have something inside {} ?

[Michael Dyck]

David Lee wrote:
> 
> I am asking why in *XQuery*  the expression {} is not equivalent to {()}

It might simply be that no-one suggested it.

> Is there a case in *XQuery* where this would be problematic ?

I don't think so.

Probably the least-impact way for the spec to accomplish this would be 
to alter the syntax of EnclosedExpr, from
     EnclosedExpr ::= "{" Expr "}"
to
     EnclosedExpr ::= "{" Expr? "}"
and then say that, if the Expr is omitted, the EnclosedExpr yields the 
empty sequence. Note that, in addition to element and attribute content, 
this would also take effect when an EnclosedExpr is used as a function 
body, which may or may not be something you'd like as well.

-Michael