What do "expenses" actually entail on property listings?

[Mark K.]

Hello, I am beginning to look at property listings online for multi-unit properties and am seeing the "expenses" vary from property to property.  Sometimes it's not even listed at all.  What exactly do the expenses entail?  

I understand it is "pro forma" but am having a tough time with the following...

• Are the expenses for a specific time period?
• Did the agent that listed this get this from the seller?
• How do I calculate expenses on a property I've never seen (aside from the usual built in expenses like property management)?
• Is there any way to truly know the expenses? I'm guessing the only way is to access the sellers books?

Below is an example of what I'm referring to...

http://www.realtor.com/realestateandhomes-detail/3...