importcomponent element information items (referred to in this
specification as importcomponent elements) are element information
items in the CellML namespace with local name equal to component,
which appear as children of import elements.
Every importcomponent 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 of any other component
element or importcomponent element in the CellML infoset.
Every importcomponent element MUST contain a component_ref
attribute in the empty namespace. The value of the component_ref
attribute MUST be a valid CellML identifier. The value of the
component_ref attribute MUST match the value of the name attribute
on a component element or importcomponent element in the
imported CellML infoset. The value of the component_ref attribute
MUST NOT match the value of the component_ref attribute on any
sibling importcomponent element.