From what I have learned, the concept of prestige class is just like multiclass. Instead of taking the levels of classes which have no prerequisites, you take the levels of a class which has prerequisites that must be met first.
And after taking the levels of a prestige class, your class can longer be considered as your original, pure class. For example, after a wizard takes the levels of Harper Scout, the character is no longer a wizard and becomes a combination of wizard and Harper Scout.
Am I understand it correctly? I know prestige classes are not counted for the multiclass penalty. I'm just talking about the "concept".
To be frankly, I'm asking this because I prefer pure class and do not want my character to lost the pureness.