SYSML2 — Add a distinguished attribute to capture the textual body of a requirement

A requirement should include a text body to capture the shall statement or other human readable requirement statement. The doc annotating element is one way to accomplish this. However, a doc element on a requirement definition is inherited by its requirement usages, but it cannot be redefined on its usage. (Note: The texts of a RequirementUsage are the bodies of the documentation of the RequirementUsage.)

The proposal is to add a distinguished attribute to capture the text body of a requirement that would replace the derived text attribute/documentation. This distinguished attribute can be redefined. This avoids a requirement usage from having both the original text in the requirement definition and the modified text in the usage.

The concrete syntax should be updated accordingly.