[captn3m0]

Let’s say a text based ad shows up in a div with the id “advert”.

A DNS based blocker will not be able to block it, but an extension or a proxy based blocker that looks at the HTML content will be able to block it.

So yeah, inject as well as as modify the HTML directly.

It could do things like shimming advertising libraries as well defanging them potentially.

[sumtechguy]

To add to that. DNS block is basically 'built in' for this type of filtering as you can just make your filter strings your list of DNS sites. It does have the downside that not everything is http. That is where a real DNS filter comes into play with known malicious endpoints. So a combination is very nice to have.

[bilekas]

Okay, that makes a bit more sense now actually!