Legendary items with affixes increasing elemental “Hit” damage should have ones that increase elemental dot damage too.
+fire damage/+burn damage ,
+lightning damage/+electrocute damage,
+cold damage/+frost burn damage,
+elemental damage/+all three types of elemental dot damage
However, “increasing elemental dot damages” aren’t where they are supposed to be on legendary helm- Horns of Korvaak.