Meaning of Explicit and Implicit Variation Point

Question

I read about explicit and implicit variation points from here, but didn't understand the meaning. Could anyone explain to me the explicit and implicit Variation Points (in OOP)?

Answer 1

Explicit variation points are markers in the code at each location where variation occurs. Annotating each variation point is one way to explicitly define variations.

Implicit variation points have no code markers indicating where they occur; therefore, implicit variation can happen anywhere.

Quoting the relevant paragraph for posterity.

Explicit variation points. Depending on the used variability mechanism and its technique, the form of variation points differs. In the mechanisms of Conditional Compilation and Frame Technology, variation points are both realized as annotated code fragments (e.g., a #ifdef block), which are explicit and easy to identify. In contrast, the variation points of the other mechanisms are implicit. For instance, variation points of Cloning are arbitrary text, and variation points of Module Replacement are typically function calls or files which also can be non-variability code.