ReadItLater-type app that saves web articles but also allows highlighting? I use Pocket and I love it as a way of saving articles to read them later, and how it allows me to browse, search, and read them easily. 

However, when I read articles, I like to create highlights (in yellow) and add annotations. Pocket doesn't offer highlighting. 

There's a great OSX app for PDFs, Skim, that highlights and annotates perfectly when I'm reading a PDF. But it would be so much better to not have to convert a web page to PDF in order to highlight and annotate it. 

I would like to be able to create my own library of archived web articles (like Pocket allows me to do) that I can tag, search, and mark up. 

Is there a "read it later" type app that will allow me to create my own library of archived web articles that I can then highlight and annotate?
A recent update of Instapaper (May 8, 2014) allows highlighting. Any highlights you create are saved into your saved version of the article and are visible online as well.