Casting

• instance of tests the type of an item against the QName of a type

• Casting changes the type of an item

• Not all casts are legal, but mostly it works like you'd expect.

• castable returns true if the cast is possible, false otherwise

• item cast as type permanently changes the type of an item

• item treat as type temporarily changes the type of the item for this expression only

if ($x castable as xs:gYear) then 
  $x cast as xs:gYear
else if ($x castable as xs:integer) then 
  $x cast as xs:integer
else if ($x castable as xs:decimal) then 
  $x cast as xs:decimal
else 
  $x cast as string