where no search utility is available to find the first use.) It also gives students a convenient review list to memorize the important acronyms introduced in a textbook chapter. Expansion at first use and abbreviation keys originated in the print era, but they are equally useful for electronic text. Jargon While acronyms provide convenience and succinctness for specialists, they often degenerate into confusing jargon. This may be intentional, to exclude readers without domain-specific knowledge. New acronyms may also confuse when they coincide with an already existing acronym having a different meaning. Medical literature has been struggling to control the proliferation of acronyms, including efforts by the American Academy of Dermatology. As mnemonics Acronyms are often taught as mnemonic devices: for example the colors of the rainbow are ROY G. BIV (red, orange, yellow, green, blue, indigo, violet). They are also used as mental checklists: in aviation GUMPS stands for gas-undercarriage-mixture-propeller-seatbelts. Other mnemonic acronyms include CAN SLIM in finance, PAVPANIC in English grammar, and PEMDAS in mathematics. Acronyms as legendary etymology It is not uncommon for acronyms to be cited in a kind of false etymology, called a folk etymology, for a word. Such etymologies persist in popular culture but have no factual basis in historical linguistics, and are examples of language-related urban legends. For example, "cop" is commonly cited as being derived, it is presumed, from "constable on patrol", and "posh" from "port outward, starboard home". With some of these specious expansions, the "belief" that the etymology is acronymic has clearly been tongue-in-cheek among many citers, as with "gentlemen only, ladies forbidden" for "golf", although many other (more credulous) people have uncritically taken it for fact. Taboo words in particular commonly have such false etymologies: "shit" from "ship/store high in transit" or "special high-intensity training" and "fuck" from "for unlawful carnal knowledge", or "fornication under consent/command of the king". Orthographic styling Punctuation Showing the ellipsis of letters In English, abbreviations have traditionally been written with a full stop/period/point in place of the deleted part to show the ellipsis of letters – although the colon and apostrophe have also had this role – and with a space after full stops (e.g. "A. D."). In the case of most acronyms, each letter is an abbreviation of a separate word and, in theory, should get its own termination mark. Such punctuation is diminishing with the belief that the presence of all-capital letters is