XQuery comments, delimited by (: and :), can be added to any query to provide more information about the query itself. These comments are ignored during processing. XQuery comments can contain any text, including XML markup. For example:

(: This query returns the <number> children :)

XQuery comments can appear anywhere insignificant whitespace is allowed in a query. If they appear within quoted strings, or directly in the content of element constructors, they are not interpreted as comments. XQuery comments can be nested within other XQuery comments.

You can also include XML comments, delimited by <!-- and -->, in your queries. Unlike XQuery comments, these comments appear in the result document. They can include expressions that are evaluated, making them a useful debugging tool. XML comments are discussed further in Chapter 21.