Maxperson
Morkus from Orkus
When the dictionary says that literature means the As, and especially the As that are also Bs, it is telling us that the word "literature" is used to mean A, but also, and especially, is used to mean the As that are Bs. There would be no point to including that second element of the definition if, in fact, there was no such distinctive and typical pattern of usage. In this case, one doesn't need to refer to a dictionary to make the point - it's not an obsecure one. If someone says, for instance, that s/he studies literature, I think most of us would assume that cookbooks and railway guides and stereo installation instructions are not on the syllabus. (Contrast if she said that she studies communication, in which case those things might well be candidate objects of study.)
What it also doesn't do, is exclude A. The use of especially still leaves A as a what literature means. Just yesterday we a bunch of new furniture arrived. My wife said, "We're going to need to watch the dogs. They like to spray to mark territory." I responded, "Yep. They do like to spray, especially the white one." To believe you guys, my response meant that our black dog suddenly doesn't mark any longer. The especially doesn't work that way. It just points out one aspect of the set, in this case spraying and in the above case literature, and call it out as greater.