If there's not already, it would be nice to be able to search for books, specifically theology books and commentaries via the author's main doctrinal persuasions. Such as if I wanted to see a list of all the commentaries that were Calvinist or Arminian in nature, then it would list only those commentaries/books. Or if a theology book's author was covenant theology or dispensational in nature, have a list/tag that shows such. Perhaps this is already capable and I don't know of it. Some commentaries are easy to know their doctrinal persuasion, but others are difficult to tell. I understand it's best to not put yourself in a "strict camp," but to study the Bible with little bias and allow the Holy Spirit to teach you, but such a feature would be nice so you could see how opposite camps would interpret a passage.