Which element participates in the combination first？

[ShaoLliang]

I have two weapon （Tenet Agendus），

When I add an ice damage mod。

The weapon of fire damage addition has become explosion (fire + ice) and electric damage。

The weapon of toxin damage addition has become magnetic  (electricity and ice)  and toxin damage。

 Please tell me which element takes precedence in the combination，Additional elements or The elements contained in the weapon itself。