There are no statements, even though some of the keywords appear to suggest statement-like behaviors.
To execute a function, the expression within the body is evaluated and its value is returned.
(...) XQuery/XPath sequences differ from lists in languages like Lisp and Prolog by excluding nested sequences.
Designers of XQuery may have considered nested sequences unnecessary for the manipulation of document contents.
Sometimes, you might also want your query to use values from a Transact-SQL variable, or parameter, to bring relational and XML data together. The SQL value will be mapped to a corresponding XQuery value and its type will be an XQuery base type that is equivalent to the corresponding SQL type.
You can only refer to an xml instance in the context of the source expression of an XML-DML insert statement; otherwise you cannot refer to values that are of type xml or a common language runtime (CLR) user-defined type.
As described in the topic Binding Relational Data Inside XML, you can use this function when you use XML data type methods to expose a relational value inside XQuery.