Regarding the specifications here: http://www.omg.org/technology/documents/formal/uml.htm
What is the difference between without and with change bars?
As for “superstructure and infrastructure”, I found out the following:
The UML infrastructure specification defines the foundational language constructs required for UML 2.1.2. It is complemented by UML Superstructure, which defines the user level constructs required for UML 2.1.2. The two complementary specifications constitute a complete specification for the UML 2 modeling language.
Where do I look into if I want to know the UML metamodel in order to know how to map a language construct into a UML model?
Change Bars: On the left hand margin you can see black bars wherever there has been a change since last version, that is why even the footer has changed as the version has. In section 7.3.32 you can see a change bar in the constraints section where something clearly changed.
Superstructure vs Infrastructure: Use the superstructure for learning more about the UML model to map like constructs to help create correct stereotypes, domain specific models using UML constructs, and creating UML profiles. This is 90% of the typical need. In fact section 18 in the superstructure covers profiles. Infrastructure is for how UML hangs together internally and is packaged up into different functional areas. It also defines parts that are not even “exposed” to the user of UML. Not typically needed unless you are going to mess with UML at the MOF level, just normally not needed and more difficult.