I've just noticed that the try/catch expression requires parens in some circumstances.

The following are allowed:

(try {$x cast as xs:integer} catch * {1}) + 1

(try {$x cast as xs:integer} catch * {1}) eq 1

Remove the parens and these expressions do not parse.

This comes about because we placed TryCatchExpr in ExprSingle:

[40]  ExprSingle  ::= FLWORExpr
                      | QuantifiedExpr
                      | SwitchExpr
                      | TypeswitchExpr
                      | IfExpr
                      | TryCatchExpr
                      | OrExpr

Perhaps it would be better located in ValueExpr:

[96] ValueExpr    ::=  ValidateExpr | PathExpr | ExtensionExpr