When it comes to common-practice notation, basically every college theory textbook explains all of the basics. But I don't know of any undergraduate theory textbook that includes a discussion of chant notation; are there any? And if so, what are they?
(I know this question is dangerously close to "requesting external resources," which is off-topic, but I think it's sufficiently separate, since I'm seeking a question with a clearly defined answer that does not require a link to said external resource.)