Certain.
The devs have stated, and experience has shown, that the presence of elemental damage is a boolean property, for purposes of intensity. 10% cold, 90% physical is just as much 100% intensity as 100% fire.
If the answer to the question is "yes", then there is a random roll to how much of the resist isn't physical. It then goes through each of the colored resists (can't remember if it's linear, or in the same order as the enhancement order - I think the latter). There is a chance of the result being 0%, or potentially 100%, that is rolled for the first. If that roll doesn't replace all of the physical resist that the initial roll indicated, then it goes to the second; then to the third, then to the last.
So, it's like
Elemental? Yes/No
(If yes, was considered a 100% intensity before the change to runics and imbuing to consider it a freebie.)
If yes, a random roll is made to determine the total amount of damage that is replaced (random 10%-100%, rounded to nearest 10%, or 11-109%, truncated resulting in 10%-100%), in 10% increments. This percentage is not determined by runic type.
Once amount of non-physical damage is determined,
Amount is rolled for the first potential elemental damage, and truncated as above, or to the total amount, if greater than the total amount. This number can be 0.
Second damage type is rolled, truncated as above, for the remaining amount.
Third Type is then rolled, as above.
The last type is handled one of two ways (not sure of which). Either it is treated as the other three, and if all the damage conversion isn't used up, it restarts at the beginning to try to use it up again (I think, but not sure, that was what was said), or all remaining elemental damage not already assigned becomes the last. (note that the latter system might make weapons with two or more elemental damage types have that last type much more often than the others.)
I can't remember if it was, Hanse, Wilki , Mr. Tact or one of the other devs that indicated this, years before bow runics existed. As it is, I'm trying to remember a post that dated from the AoS era, that was lost in the Spring 2008 Stratics Crash.
