No matter how skillful a teacher may be, if his/her only knowledge of a subject is what is written in the textbook, then that teacher will be greatly hindered in instructing any students in that topic. For example, a teacher may have thoroughly studied, and even memorized, an auto repair manual. But if that teacher had never done any auto repair at all, he would ge greatly limited in his ability to teach his students how to repair cars. The main thing that he could teach  them would be how to study and get to know the text in the repair manual.

Just because a writing mentions another writing doesn't make the first writing to be the second writing. For instance, if I were to write a letter telling how valuable the Rodale cookbook is, that doesn't make my letter into the Rodale Cookbook. Here's another example. If I write an essay about the history of America, and if I quote Poor Richard's Almanac, my essay would not become the Poor Richard's Almanac. The fact that a written document quotes or mentions a fact or an item doesn't make that document to