What are the differences between the difficulty levels in the Campaign and Skirmish modes?

Question

What are the differences between the Standard, Moderate and Hard difficulty levels in the Campaign mode?

What about between Easiest, Standard, Moderate, Hard, and Hardest in the Standard/Multiplayer Game (Skirmish) mode?

If the AI changes its behavior or strategy depending on the difficulty level, please include that info.

Also, does the AI "cheat" (by giving itself additional resources, etc.)? If yes, what cheats does it do and at what difficulty level(s) does it cheat?

EDIT: In this answer to my question below, most of the questions have already been answered. That leaves the question, "What are the differences between the Standard, Moderate and Hard difficulty levels in the Campaign mode?" to be answered or expounded upon.

Answer 1

Distance an enemy unit must be within when the computer player unit looks for a new target:

easiest:    LOS (can be modified by sn-easiest-reaction-percentage)
easy:       LOS (can be modified by sn-easier-reaction-percentage)
moderate:   LOS * 2
hard:       LOS * 2
hardest:    LOS * 2

Computer players ignore relics on the easiest level.

If a non-exploring computer unit gets attacked, the computer player's attack delay is modified:

easiest:    allow attacking one minute ealier
easy:       allow attacking two minutes earlier
moderate:   allow attacking immediately
hard:       allow attacking immediately
moderate:   allow attacking immediately

After a wolf kills a unit, have it gorge itself (not attack again) for:

easiest:    35 seconds
easy:       30 seconds
moderate:   25 seconds
hard:       20 seconds
hardest:    15 seconds

Distance a unit must be within when a wolf looks for a new target:

easiest:    LOS * 0.5
easy:       LOS * 0.75
moderate:   LOS * 2
hard:       LOS * 2
hardest:    LOS * 2

Source: This Reddit /r/aoe2 post, which refers to the Official Computer Player Strategy Builder Guide (cpsb.doc) in the AOE 2 CD 'GOODIES' folder.

Answer 2

Not 100% if it does anything other than improving the AI in the campaign mode.

In skirmish mode it improves the AI, and being attacked by the enemy and how often it happens depends on the difficulty. For example; If you play on Easiest in Skirmish mode, the enemy will never attack you, the higher you go in difficulty makes them attack you and more often/earlier in the game.

They don't use "cheats" for resources and you can make them run out of resources just as any other game if you/the game lasts long enough.