Graphic: Extending Visibility

The above graphic clarifies the principle of extending the visibility of package elements over several levels.

P1 and P2 are two main packages. The object IF_1 (from the sub-package P1_2) is passed up to the interface I1 (of the main package P1) using the package interface I2_3 through I1_2. This makes it visible in P2. Conversely, the element FB_1 is only added to the package interface I2_1, so it is not passed up to the next level. This means that its visibility is not extended any further; it is limited to sub-package P1_1. In contrast, TAB_1 cannot be seen outside P1_2, since it has not been added to any of its package interfaces.