Minimum Requirements for weapons

What happens if you don't meet the minimum requirements on a weapon?

For instance. I have a staff which has a necro attribute requirement but I am not a necro. Can I use it? Does it do damage? How much will it do? What about any other mods on the staff (does it just apply to the line that it's listed on, or to all lines)

you can use it but the damage output of that weapon no matter what the stats say will be the min damage 3-4

You do a lot less damage if you don't meet the requirements, but you can use the weapon.
Also for abilities on the weapon (like 20% chance for +1 blood magic for ability) if it has a requirement you don't meet it won't work.