The ``connection`` element information item
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``connection`` element information items (referred to in this specification
as ``connection`` elements) are element information items in the CellML
namespace with local name equal to ``connection``.

Specific information items
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1. Every ``connection`` element MUST contain exactly one ``map_components``
   element.

2. Every ``connection`` element MUST contain one or more ``map_variables``
   elements.