many cases; e.g. AIDS stands for acquired immuno-deficiency syndrome which is not a proper name, while Aids is in the style of one. Some style manuals also base the letters' case on their number. The New York Times, for example, keeps "NATO" in all capitals (while several guides in the British press may render it "Nato"), but uses lower case in "Unicef" (from "United Nations International Children's Emergency Fund") because it is more than four letters, and to style it in caps might look ungainly (flirting with the appearance of "shouting capitals"). Numerals and constituent words While abbreviations typically exclude the initials of short function words (such as "and", "or", "of", or "to"), this is not always the case. Sometimes function words are included to make a pronounceable acronym, such as CORE (Congress of Racial Equality). Sometimes the letters representing these words are written in lower case, such as in the cases of "TfL" ("Transport for London") and LotR (The Lord of the Rings); this usually occurs when the acronym represents a multi-word proper noun. Numbers (both cardinal and ordinal) in names are often represented by digits rather than initial letters, as in "4GL" ("fourth generation language") or "G77" ("Group of 77"). Large numbers may use metric prefixes, as with "Y2K" for "Year 2000" (sometimes written "Y2k", because the SI symbol for 1000 is "k", not "K", which stands for "kelvin", the SI unit for temperature). Exceptions using initials for numbers include "TLA" ("three-letter acronym/abbreviation") and "GoF" ("Gang of Four"). Abbreviations using numbers for other purposes include repetitions, such as "A2DP" ("Advanced Audio Distribution Profile"), "W3C" ("World Wide Web Consortium"), and T3 (Trends, Tips & Tools for Everyday Living); pronunciation, such as "B2B" ("business to business"); and numeronyms, such as "i18n" ("internationalization"; "18" represents the 18 letters between the initial "i" and the final "n"). Casing of expansions Authors of expository writing will sometimes capitalize or otherwise distinctively format the initials of the expansion for pedagogical emphasis (for example, writing: "the onset of Congestive Heart Failure (CHF)" or "the onset of congestive heart failure (CHF)"), but this conflicts with the convention of English orthography, which reserves capitals in the middle of sentences for proper nouns; and would be rendered as "the onset of congestive heart failure (CHF)" when following the AMA Manual of Style. Changes to (or wordplay on) the expanded meaning Pseudo-acronyms Some apparent acronyms or other abbreviations do