units element information items (referred to in this specification as
units elements) are element information items in the CellML namespace
with local name equal to units, and with either a model element or
a component element as their parent.
Every units element MUST contain a name attribute in the empty
namespace. The value of the name attribute MUST be a valid CellML
identifier.
Where the parent of the units element is a model element,
the value of the name attribute MUST NOT be identical to the name
attribute of any other units element child of that model element, or
of any importunits element in the CellML infoset.
Where the parent of the units element is a component element, the
value of the name attribute MUST NOT be identical to the name
attribute of any other units element child of that component element.
In any case, the value of the name attribute MUST NOT be equal to a
cell in the name column of the Built-in units table.
A units element MAY contain a base_units attribute in the empty
namespace. If present, the value of the base_units attribute MUST be
equal to either yes or no. If the attribute is present and equal to
yes, then the following paragraph does not apply.
A units element MAY contain one or more unit element children.