The UML method to extend UML (basic) components with a special meaning
is by using stereotypes. A stereotype defines a special usage of a model
element. For example: a class that's used as a controller can be
assigned a stereotype "controller". Stereotypes are always enclosed
Creating a stereotype starts by the creation of a Profile normally. Although stereotypes can be created in every package, it's a good habit to use Profiles for that. Next a Metaclass has to be created. The metaclass will tell the stereotype on which kind of elements it is applicable. A Stereotype can be connected to the Metaclass by means of an Extension relationship.
Stereotypes can be applied to basically all elements in a model.
Stereotypes can contain attributes, as shown in the diagram above. Those attributes can be filled in the Element Editor. This allows for enormous flexibility. In most cases, especially if some sort of program logic has to be generated from the models, it is very handy to define special behaviours to classes and other elements by means of stereotypes.