.. _zero-or-one:

===========
zero-or-one
=========== 

Returns a sequence if it contains zero or one items, otherwise errors

Description
~~~~~~~~~~~
The fn:zero-or-one function returns $arg if it contains zero or one items. 
Otherwise, the error FORG0003 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**
   * - zero-or-one( () )
     - ()
   * - zero-or-one('a')
     - a
   * - zero-or-one( ('a', 'b') )
     - Error FORG0003

See Also
~~~~~~~~

.. toctree::
   :titlesonly:
   :glob:

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