I'm a new developer in salesforce, and just realize that there are some "attribute fields" (i don't know if that's the correct name) but i cant figure it out where are those field "set"/"declare".
Fields like "isWon" or "isClosed" in the Opportunity Object, i just cant find where are declared ( i cant see those fields in the Opportunity - "Fields & Relationship section, BUT i can see those fields/attributes in the formula settings for validation rules).