Clarity lets herself into the library, intent on following up on that prediction as soon as she's worked out the categorization.
"Oh, hello!" she says, looking up as Clarity comes in. "Are you here for a book?"
"Uh... among other things. I'm in Ponyville on an errand for the Princess and I'm supposed to stay here until tomorrow."
"Oh! Okay," says the little pony. "That's odd, I wonder why the library? I guess it's free and everything, but... are you usually a librarian?"
"No. I like books, but I'm not actually a librarian. I do need to do some research incidentally, though." She starts peering at some shelves, trying to figure out what organizational system is at play here. "I'm Clarity Bell, by the way."
"I'm Blueberry! What are you looking for?" she asks, standing up. "I've been coming here practically my whole life, so I know where everything is."
"Unfortunately I was interrupted by the errand so I don't have much to go on. Key words include -" Clarity produces her current notebook. "Mare in the Moon, or, Nightmare Moon; and the Elements of Harmony." What kind of classification system is this? It doesn't seem to be arranged by author or in subject groupings. Is this literally alphabetical by title? Wow.
It is titled The Elements of Harmony: A Reference Guide.
"Oh, cool, that's exactly what I needed. Who organized this place? Is it, in fact, alphabetical by title less leading articles, or is there some nuance that I'm missing?"
"The last librarian organized it. But then she moved to Manehattan. The shelves that are alphabetical by title are because there's no author recorded for those books; if you start over there," she points a hoof, "it's nonfiction alphabetical by author, then fiction alphabetical by author that stops over there and starts again up there on the next floor, then a bunch of things that Page Turner never got around to filing properly in no particular order on that shelf way up there."
Okay. Six Elements of Harmony, only five known: laughter, generosity, loyalty, kindness, honesty. Known to whom? The unspecified author of this book, apparently. Oh, hay, why didn't the Princess listen to her? The other book said she used the bucking things. She could probably list them all, and tell Clarity where they were, in less time than it had taken to chide her and tell her to make friends. And then Clarity would at least have an idea of what to do if some disaster did happen to occur at the Summer Sun Celebration.
Oh, this book knows where they were last seen, apparently. Last known location, palace of the pony sisters, located in what had become by the time of this book's publication the Everfree Forest.
Eeugh. Clarity has heard of this forest; it is no doubt serving useful ecological purposes, but it isn't exactly a comfortable prospect for traveling through.
Celestia was unworried; the elements sound vaguely from the language of this book like they might require special status of some kind to use at all; and if they were that important Clarity vaguely doubts they'd have been left to decay or crumble or undergo whatever deterioration process applies to the unspecified material in a disused castle. So she decides they're probably not worth running out to fetch right now. She might not make it there; she might not need them for anything; if she did she might be unable to handle them to any useful effect; and they might not be all they're cracked up to be. But she feels better for having been able to consult the reference and is glad she left time for it.
"More or less. It's not as complete as one might hope, but it's probably the best thing available right now."
"I saw them referenced in a book I was reading earlier and wanted to follow up; I wasn't strongly expecting to find any particular facts because I didn't know what they were."
"Oh, I see. The book is kind of vague. It talks about how powerful they are, but not what they're for or how to use them. Not much of a reference guide, if you ask me."
"It really isn't. I don't suppose there's another book mentioning them that you've run across?"
"I can't think of one offhoof, but I haven't read every book in this library," she says. "Just most of them."
Clarity looks around the vast array of books in the library. "You must read pretty fast," she says, trotting up to the top floor where the librarian living quarters are to finally offload her saddlebags.
"Do you want to take over for the old librarian when you grow up?"
"I guess the library would have to stay unstaffed for quite a while to still have the position available in a few years, though." Clarity locates the disorganized shelves and scans them in case there's something else Elements- or Mare-in-Moon related but finds nothing.
"Well, you clearly know how to perform at least one librarian-designated task already, I would have spent hours looking for that book on my own."