In plant design we sometimes have to model "operational modes", whereas in product catalogs we often see "options". Both are in fact identical, and hence they are modeled identically.
An operational mode is a way the facility must function, and hence be configured.
Options in a product catalog are ways in which a product may be configured.
It is important to note that there must be a choice between more than one operational mode or option. If not, then the optionality is modeled using cardinalities.
This paper explains the model, as a sequel to the paper "Life cycle of a Class".
An example model:
Mode 1 and Mode 2 in above example could be the Modes of Operation ("cases") "Normal Operation" and "Regeneration". For each of these two modes a subclass of the requirements class of P-101 is defined. Please keep in mind that the information that is common for both modes is to be stored against the common superclass.
An unexpected example
In the topic of mapping a line list the situation occurred that a line seemingly has two sizes. In fact that line has one size and one smaller size for drains and vents. That is a case like in above diagram, where X1 is one size and Y1 the other size. The rest of the requirements is the same for both.