.. _exactly-one:

===========
exactly-one
=========== 

Returns a sequence if it contains exactly one item, otherwise errors

Description
~~~~~~~~~~~
The fn:exactly-one function returns $arg if it contains one and only one item. 
Otherwise, the error FORG0005 is raised. This function is useful when static 
typing is in effect, to avoid apparent static type errors.

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   :header-rows: 1

   * - **Parameters**
     - **Description**
   * - arg:item()
     - 

Examples
~~~~~~~~
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   * - **XPath**
     - **Results**
   * - exactly-one( () )
     - Error FORG0005
   * - exactly-one('a')
     - a
   * - exactly-one( ('a', 'b') )
     - Error FORG0005

See Also
~~~~~~~~

.. toctree::
   :titlesonly:
   :glob:

* :ref:`one-or-more`.
* :ref:`zero-or-one`.