[Unsolved] Channel Types

What exactly do the different Channel types do?

Visible
Targeting Image
Physical Spell
Universal Spell
Unique Cast

I think, that some specific types of damage deals more/less damage to specific armor type.

Visible - If active, you can see the ability button in the unit's command card.
Targeting Image - If active and targeting type is point, it will display a circle, cf Blizzard vs Breath of Fire.
Physical Spell - If active, can be cast on magic immunes but not etheral units.
Universal Spell - If active, can be cast on magic immunes and ethereals.
Unique Cast - If active, multiple units selected that have the ability will not fire them all at the same time if ordered.

I'm not completely sure about the "Physical" and "Universal Spell" fields though.