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doc_what_is_required_attribute Class Reference

## Detailed Description

  SBML Level 3 requires that every package defines an attribute named "required" on the root `<sbml>` element in an SBML file or data stream. The attribute, being in the namespace of the Level 3 package in question, must be prefixed by the XML namespace prefix associated with the package. The value of the "required" attribute indicates whether constructs in that package may change the mathematical interpretation of constructs defined in SBML Level 3 Core. A "required" value of `true` indicates that the package may do so. The value of the attribute is set by the Level 3 package specification, and does not depend on the actual presence or absence of particular package constructs in a given SBML document: in other words, if the package specification defines any construct that can change the model's meaning, the value of the "required" attribute must always be set to `true` in any SBML document that uses the package.

The XML namespace declaration for an SBML Level 3 package is an indication that a model makes use of features defined by that package, while the "required" attribute indicates whether the features may be ignored without compromising the mathematical meaning of the model. Both are necessary for a complete reference to an SBML Level 3 package.