Caret (proofreading)
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Caret [ˈka-rət, ˈker-ət], sometimes spelled carat[dubious – discuss], is the name for the symbol ^ in ASCII and some other character sets. Its Unicode code point is U+005E, and its ASCII code in hexadecimal is 5E. Strictly speaking, the caret character in common use is actually referred to in the Unicode standard as the "CIRCUMFLEX ACCENT"; the Unicode character named "CARET" is actually a distinct, much less common character, at code point U+2038 (‸). There is also a combining mark, U+0302 "COMBINING CIRCUMFLEX ACCENT", which is used when a circumflex accent is to be added as a diacritical mark to another letter. However, the term "caret" is most frequently used to refer to the first of these. It is also a mark used by an author or editor to indicate where something is to be inserted into a text. On Mac OS 9 and earlier it was referred to in official documentation as a 'hat'.
Uses and history
The caret was originally used, and continues to be, in handwritten form as a proofreading mark to indicate where a punctuation mark, word, or phrase should be inserted in a document. The term comes from the Latin caret, "it lacks", from 'carēre', to lack; to be separated from; to be free from. The caret symbol is written below the line of text for a line-level punctuation mark such as a comma, or above for a higher character such as an apostrophe; the material to be inserted may be placed inside the caret, in the margin, or above the line.
The caret is also found on some typewriters, where it is used to denote a circumflex accent in languages which require it, such as French and Portuguese.
In statistics, the caret is used to denote an estimator or an estimated value, as opposed to its theoretical counterpart. For example, in the context of errors and residuals, the "hat" over the letter ε indicates an observable estimate (the residuals) of an unobservable quantity called ε (the statistical errors). It is read x-hat or x-roof, where x is replaced by the character under the "hat".
In mathematics and physics, a caret appearing above a letter indicates a unit vector (a dimensionless vector with a magnitude of 1), or an operator.
In mathematics, a caret can signify an exponent (3^5 for ) where superscript is difficult or impossible (such as on some graphing calculators).
In mathematics, a caret placed above an element of a set can signify that that element has been removed from the set.
In programming languages the caret is used to signify exponent, to represent a bitwise XOR operator, or to represent a string concatenation operator, among other uses. The use of as exponent can be traced back to ALGOL 60, which expressed the exponentiation operator as an upward-pointing arrow, intended to evoke the superscript notation common in mathematics. The up-arrow character was codified as character 5E in the original 1963 version of the ASCII standard; however, this was a short-lived placement. The 1965 ECMA-6 standard replaced the up-arrow with the currently-used caret (and the left-arrow with the underscore); two years later, the second revision of ASCII followed suit, due to pressure from international standards committees requiring the character's presence as a diacritical mark (the circumflex). The caret is commonly used to signify control characters in caret notation. Pascal uses the caret when dereferencing pointers.
In regular expressions the caret is used to mark the beginning of a string, or the beginning of a line within that string (depending on the regular expression dialect and specified options); if it begins a character class, it indicates that the inverse of the class is to be matched.
In logic the caret is used as a propositional operator to symbolize logical conjunction otherwise known as an "and" statement. e.g. pq. Ideally, this wedge symbol is different from the caret, see ∧.
The caret has been registered as a service mark by HydraByte, Inc. to identify various web-based services.
Other meanings
The term caret is also sometimes used in graphical user interface terminology where it means a text insertion point indicator, frequently represented by a blinking vertical bar. In this context, it may be used interchangeably with the word cursor, although the latter term is often reserved for a mouse pointer.
In music notation, a caret placed above a note indicates marcato denoting a special form of emphasis or accent. The inverted caret (a narrow "v") indicates the marked note be performed up-bow for string musicians especially: violin, viola, cello and contrabass.