Ascendancy
Main skill
Filters
The rules
The skill you roll has to be your primary source of damage. Everything else is yours to choose: supports, auras, heralds, a single-target finisher, a movement skill.
Gems are not locked to classes in Path of Exile 2. A Warrior can roll a bow skill, and if the weapon and attribute requirements can be met, that is a legal roll. The result panel says when a combination is going to fight you.