libSBML Perl API
libSBML 5.10.0 Perl API
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NULL
if no units have been declared and no defaults are defined by the relevant SBML specification.Note that unit declarations for Compartment objects are specified in terms of the identifier of a unit, but this method returns an object , not a unit identifier. It does this by constructing an appropriate UnitDefinition object. For SBML Level 2 models, it will do this even when the value of the "units" attribute is one of the special SBML Level 2 unit identifiers "substance"
, "volume"
, "area"
, "length"
or "time"
. Callers may find this useful in conjunction with the helper methods provided by the UnitDefinition class for comparing different UnitDefinition objects.