The ``component`` element information item
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``component`` element information items (referred to in this specification
as ``component`` elements) are element information items in the CellML
namespace with local name ``component``, and which appear as a child of a
``model`` element.

Specific information items
--------------------------

1. Every ``component`` element MUST contain a ``name`` attribute in the empty
   namespace. The value of the ``name`` attribute MUST be a valid CellML
   identifier. The value of the ``name`` attribute MUST NOT be identical to
   the ``name`` attribute on any other ``component`` element or ``import component``
   element in the CellML infoset.

2. A ``component`` element MAY contain zero or more specific information
   item children, each of which MUST be of one of the following types:

   a. A ``units`` element;

   b. A ``variable`` element; or

   c. An element information item in the MathML namespace, and with
      local name ``math``, which MUST be the top-level of a content MathML
      tree, as described in `MathML 2.0 <http://www.w3.org/TR/2003/REC-MathML2-20031021/>`_.