Book Cipher

A book cipher, sometimes called the Ottendorf cipher, is a cipher where letters or words are selected from a particular piece of written text that acts as a key, and are transformed into strings that require reference to the larger piece of text in order to extract their meaning.

Background
See also: Book cipher

Puzzle Application
A book cipher takes a particular piece of text (a book, essay, article, or even a piece of text present in the puzzle itself) and uses it as the 'key' for extraction. Everything extracted using it ends up coming directly from the book, either in the form of whole words or individual letters. When used to extract entire words, it's more likely to result in an Intermediate Clue Phrase or Final Clue Phrase, while individual letters may be used to extract a final answer. Since any given individual letter is more likely to occur across a piece of text than a particular word, it makes it much easier to produce an answer using the former than the latter unless someone writes a piece of text specifically for use in a particular puzzle.

The most common form of book cipher uses multiple numbers to represent individual words or letters, with each number indicating parts of the work. For larger texts, this could be Chapter/Page/Word, Page/Paragraph/Word, Page/Sentence/Word, or something similar. Single-page texts may instead choose to count lines or sentences before going into either words or individual letters.

Regardless of how long a text is, an author may also choose to use single-number codes, indicating the position of a particular word in the total word count, or a particular letter in the character count. The larger the text gets, the less viable this method ends up being, but in hunts with high expected difficulty it can still show up every once and a while. Example (using the Puzzle Application section above): 01-03-30 / 01-04-28 / 03-01-07 / 02-02-11 First number is paragraph. Second number is sentence. Third number is word. FINAL / ANSWER / IS / PARAGRAPH

Notable Examples

 * - This puzzle uses the book Through The Looking Glass, and instead of using a multi-number code, it uses word count directly. As a result, solvers end up having to identify what the 25221st word is, among others, making for a titanic task of counting.
 * - While the use of the code only occurs partway through the puzzle, it's an interesting use. Rather than just giving solvers a series of code numbers, the puzzle presents them with an audio clip of pieces of songs from the musical Hamilton, each containing a number in the lyrics. By taking the numbers from the lyrics along with the track number of the song, solvers can find words in the Federalist Papers, taking the Nth word of the Xth paper, where N is the number in the lyrics and X is the track number.
 * - Rather than using a pre-existing piece of text, this puzzle requires solvers to use the text contained in the fake crowdfunding projects on the puzzle page. In addition, they aren't given the numbers right away, and must calculate them based on the goals of each of the projects, then split them into two-digit numbers to take those words from each block of text.