I was researching the subject and I came across that this system works for sentinels. But I had a doubt, the companions (vulpa, kavat, kubrow) also have precepts mods, does this system work the same way? And for primary, secondary and melee weapons, is there an order to equip, as an exception to create elements?
(Precepts mods have the polarity " [- ", and the order makes a difference when activating sentinels abilities)
Not really what you're asking for, but for anyone rolling rivens and end up with multiple elements, this is how elements are combined: The lower if the two enements takes priority when combining with another elemental mod placed ahead of it.
If your riven is heat (top) + cold (bottom), you can throw a toxin mod before the riven to make viral + heat. If the riven was placed ahead of the toxin mod, you would have blast + toxin.
I can confirm Kubrows adhere to this precept system as well. My Raksa will either restore my shields or stun enemies with Howl depending on which is first.
As for weapons, if you mean how to combine elements, the priority goes from top left to bottom right.