How do leaders gain experience?

Taken from the 00_defines.lua within the Stellaris folder, I found these values:

Governors

• Clearing a Tile / Constructing a building gives 50% of the resources spent building or clearing.
• Having a planetary edict gives 5% of the Edict's cost each month the edict is active
• 8 exp for each Pop born
• 3.5 exp each month for governing a Sector

Scientists

• 350% bonus xp if researching within the field of their expertise
• 18 xp per planet surveyed
• 100 xp for discovering an anomaly
• 100 xp from completing a special project (in addition to the XP special projects can reward themselves)
• .35 xp * scientist level / day of "Assist Research"

Admirals & Generals

Admirals & Generals gain XP based on the ships / armies killed & lost, though the define doesn't have exact formulas. I'd wager Military power for fleets, but not sure how Army XP might be calculated.

I'm guessing that cost-reducing effects reduce experience gain as well, though that probably warrants more testing.

I don't know much about governor and how they earn experience since most of my time were spent surveying and manage research. Even when I manage planets I just look at the building tile screen and don't pay attention to Governor.

That said I assume most of the experience would come from building stuff. Because I notice that level up occur when a building/upgrade is done.

Furthermore if you have trouble giving your governor more experience. You can research technologies to raise your leaders overall lifetime (chance of dying young goes down).