Sorry, all this love is making me a little misty. I should move on. The above lines may be a bit hard to look at, but they're really no big deal. They are used in a DTD to define attributes and entities in XML documents. Anyone who's dealt with HTML knows these terms pretty well.
Attributes are the items within HTML tags that describe the tag more accurately.
As you'll see on the following pages, the use of attributes in XML documents is pretty similar. There's nothing terribly new about entities, either. An ampersand and semicolon surrounding a certain string of text are used to represent another character or set of characters. That leads inevitably to added syntax, though not too much. Once you know it, you'll be able to get through any XML document without choking.