How do mastery skills work?

[shed]

So from what I know, each class gets a skill that you can keep permanently after you master it, but also have skills inherent to that class. For example, if I go through mercenary and get vantage as a mastery skill, then go to swordmaster, will vantage take up 1 of the 3 slots allotted for class skills? Also since some classes come with 3 class skills, does that mean you can't use any of your previously unlocked mastered abilities with that class or can you take out innate abilities?

[BastienSoul]

Mastery abilities aren't considered Class abilities- they're grouped with the Skill Level abilities (the ones you can equip up to five of).

[IzzyFresh]

Skills gained through Mastery become equippable skills (. Class skills are seperate. Example HP +5 is a master skill.