Internal requirements in Enterprise Architect are element responsibilities. They are defined on the 'Requirements' page of the element 'Properties' dialog.
Internal requirements form the functional requirements of the system to be built. The meaning of the requirement can vary depending on which element is the host; for example, a business process requirement might mean something different to a Use Case requirement, which again might mean something different to a Class requirement.
For example, an internal responsibility to enable the user to login to the system has been defined for the Login Use Case. This is a responsibility of the Use Case - an action it is responsible for carrying out - and it applies only to this Use Case.
The significant parameters (or, in Requirement Management terms, attributes) are the Type, Status, Difficulty and Priority. Whilst you can provide a detailed description of the responsibility in the 'Notes' field, there is more scope in the name ('Requirement' field) to define the nature of the responsibility. An additional field, 'Stability', indicates the probability of the requirement changing; high stability means a low probability of change.
The example Use Case also has connections to two external requirements, which are system functions that the Use Case implements either in full or in part. You can convert an internal responsibility into an external requirement.
You can also create internal responsibilities for an element using the Scenarios & Requirements window. A responsibility created in the window displays in the element 'Properties' dialog, and vice versa.