Trying to understand filter envelope

[Headfirst]

I am a beginner with the Virus TI and I was wondering if someone can explain in simple terms how the filter envelope amount works.
I mean, you create your envelope and then you decide the amount of filter envelope. What does the envelope amount exactly mean? Is it an offset to the cutoff you have selected? For example, you set the cutoff to 40. Then you do full envelope amount. Does this mean that the attack goes from 40 to (40+ full envelope amount) and the release goes back from (40 + envelope amount) to 40?
I hope someone can clarify this for me. The Virus manuals were not of much help to me with regards to that.