How does Adblock Plus work?

[TomaszK1]

Ok. I am sure someone has answered this somewhere, but I can't seem to find it. YES I googled. My hypersomnia is kicking in, so I am typing it up before I fall asleep:

-- When ABP blocks content, does it actually just hide it/prevent it from displaying, or does it modify the http requests?
I think that with the element hiding, frames, etc., it downloads the entire page, but doesn't display the unwanted elements.
But, how is it with scripts, images, flash, video, etc.?

What I am asking is, do the pages load faster/use less bandwidth on the account of NOT downloading elements in the first place, or, do they download the same amount of data, but only LOOK cleaner because of modifying what is actually displayed and how?

I just wanna be clear... I was gonna test it, but my three old laptops don't amount to one good computer, so I just thought I'd come out and ask.
Thanks!
-Tomasz

[TomaszK1]

It is actually the opposite: an ad can detect if it is hidden, but not if it is blocked.

Now, that is really interesting..., ziutek: -Can you explain how it actually works? I always thought it worked the way SierraSonic summed it up, so I am stumped...
-Tomasz

How could they tell if they are hidden? The page is done loading, the view is counted, then it is hidden afterwards. I don't see how...

Above quotes come from the following discussion thread: - Greylist Idea | http://sn.im/v569w

[Michael]

Adblock Plus has two types of filters: element-hiding filters and blocking filters. Element-hiding filters, identified by the presence of one of more hash symbols (#), generate a stylesheet which is automatically applied to a given page and only hide the unwanted content. Blocking filters prevent items from being downloaded in the first place.