| '''Summary'''
|Returns a materialized instance of the specified {{Code|$value}}:<br />
* if an item is streamable, its value will be retrieved, and a new item containing the value will be returnedcached.
* other, non-streamable items will simply be passed through.
Materialization of a streamable value is advisable if a value is to it may not be processed more than once, and is expensive to retrieve. It is get mandatory whenever a value is invalidated before available anymore when it is requested will eventually be required (see the example below).
|-
| '''Example'''
|In the following example, a file will be deleted before its content is returned. To avoid a "file “file not found" found” error, the content will first be materialized:
<pre class="brush:xquery">
let $file := 'data.txt'