Appendices can be written by you (no references necessary) or adapted from somewhere else (reference required). The rules apply. Appendices can be used for content that is useful, supportive, or necessary but would otherwise clutter, break up, or detract from the narrative. They can also include material that only makes sense in context. As with all other parts of the book, copies of appendices should be kept (especially if they are being used as evidence in court). It is recommended that a copy of each appendix is kept separately to ensure that more than one copy isn't lost.