What abilities can be blocked by sivir's/nocturne's spell shield?

Mainly, im wondering what ultimates would be blocked, and other spells that have long casts. But if you have a list that would be nice.

Solution 1:

• Spell shields block all activation of spells (Starts of channels included).
• They do not block DoTs during the effect.
• They do not break targeted channeled effects (Fiddle's drain as an example)
• They do block spells of any type as long as it's a targeted single-hit spell (Magical, Physical and On-Hit effects) (For Requiem, the shield can be cast to block the damage part post-channel)
• They do block ONE tick out of series of persistent damage abilities. (Panth's HSS, Kennens Maelstrom.)

There are several things I'm still not sure of, such as how Viktor's CC field and Ultimate are affected, or how the shields reacts to on-hit effects.