Is there a guide on how to do this with sites that are paywalled? For example how do I use this with NYT or WSJ? And any tricks on identifying the main content?

Is there a guide on how to do this with sites that are paywalled? For example how do I use this with NYT or WSJ? And any tricks on identifying the main content? Or do you just have to deal with that being different for each site? How do the reader modes in browsers do it?