Working from a data sheet reference design a 47nF/X 250V capacitor is recommended.
What makes a capacitor an X capacitor? From some googling i've found that X capacitors are meant to go across mains. From some vague references they are metalized film capacitors because they are self healing.
Would any metalized film capacitor be an X capacitor as long as the voltage rating is met or exceeded, or is there some other specific rating that officially makes it an X capacitor?
Would a data sheet specifically say "X" capacitor or is there some other subtle way that it would be listed?