What is an upgrade modifier?

[Robbb]

I was reading the queensland barracks prizes thread and I have cement factory level 10 to reduce upgrade prices but what are upgrade modifiers? What other reduction cost there is besides the cement factory?

[PITA4PRES]

Sometimes prizes from WD events may provide an additional reduction in building and/or upgrade costs in addition to the cement factory. I have an additional 2% from the war on Poland.

[MWMike]

Certain boost units provide a discount in building upgrades. An example is the ANZAC Bridgin unit. It is the top 250 reward for the battle of Australia and provides 5% upgrade cost. Hope this helps.