My the specific source type I want to cite is not covered in the citation manual. What should I do?
Answer
Information evolves faster than citation manuals can keep up, so this is a normal situation. The main goals of citation are to give credit to the words and ideas of the author/s who created them and to enable other people to track down the sources you've used. If you've checked the citation manual and can't find the specific guidance you need, first identify the type of source in the manual that most closely resembles the source you need to cite. For example, if you're citing a stand-alone element within a book (an essay, preface material, etc.), it may make the most sense to use the "book chapter" citation style as a template. Follow along as closely as possible to that template, while making the necessary modifications (you may have to skip over a typical citation element for book chapter that doesn't exist for the source you have). When in doubt, lean on the goals of crediting the author/s and enabling others to track down the source.