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| {| class="wikitable" align="right"
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| ! <small>description</small> || character || Unicode || HTML
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| ! rowspan="2" | overline
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| | ‾ || U+203E || &oline;<br>&#8254;
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| |-
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| | ◌̅<br><small>combining</small> || U+0305 || &#773;
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| |-
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| ! rowspan="3" | macron
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| | ¯ || U+00AF || &macr;<br>&#175;
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| | ◌̄<br><small>combining</small> || U+0304 || &#772;
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| | ˉ<br><small>spacing</small> || U+02C9 || &#713;
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| |-
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| |}
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| An '''overline''' or '''overbar''' or '''overscore''' (coined in analogy to [[underline]] and [[underscore]], attested for mathematical notation since 1899), refers to the [[typographical]] feature of a line drawn immediately above the text, for example used to indicate Roman numerals multiplied by a thousand, or medieval [[sigla]]. Specifically, a line drawn over one symbol is a [[macron]], and a line over a collection of symbols is a [[vinculum (symbol)|vinculum]]. Marking one or more words with a continuous line above the characters is also described as "[[overstriking]]".
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| In [[Unicode]] the overline is represented by {{unichar|203E|overline}}, and always functions as an independent symbol. The character {{unichar|0305|combining overline|cwith=◌}} allows an overline to be placed over any character (as with any [[combining character]], it appears over the preceding character: for example, x̅, compared to x‾). A series of overlined characters usually results in an unbroken line, depending on the font (for example, 1̅2̅3̅).
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| A similar character is {{unichar|00AF|macron|nlink=Macron}} (also called "overbar"), and also has a combining variant, {{unichar|0304|combining macron|cwith=◌}}, as well as a spacing modifier variant, {{unichar|02C9|modifier letter macron}}. The macron characters are shorter than their "overline" counterparts, and a series of macron characters usually does not result in an unbroken line (for example, 1̄2̄3̄). Unlike overline, the macron is present in the [[ISO/IEC 8859-1]] and [[MS-DOS]] [[Codepage 850]] encodings. Depending on the context in which it is used, the overbar has different meanings. The table to the right gives a summary of the different Unicode characters.
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| For East Asian ([[CJK]]) computing, {{unichar|FFE3|fullwidth macron}} is available. Despite the name, Unicode maps this character to both the {{unichar|203E|overline}} and the {{unichar|00AF|macron}}.<ref name="UnicodeFull"/>
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| The Unicode character {{unichar|070F|Syriac Abbreviation Mark|nlink=}} is used to mark in [[Syriac]] text a special overline with a dot at each end and the center, stretching from the position of the character to the end of the word. This line traditionally marks abbreviations and numbers. However, most computer systems do not render this line correctly or at all.
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| ==Math and science==
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| In mathematics, an overline is used primarily in two situations: either to indicate a [[line segment]]:
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| * <math>\overline{\rm AB}</math>
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| or [[repeating decimal]] value:
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| * {{frac|1|7}} = 0.{{overline|142857}} = 0.1428571428571428571...
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| Since it is not always possible to format the number so that the overline is over a certain digit, it is often placed to the left of the digits that repeat:
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| * 3.¯3 = 3.{{overline|3}} = 3.333333333333...
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| * 3.12¯34 = 3.123434343434...
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| The overline is also used to indicate a [[sample mean]]:
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| * <math>\overline x</math> is the average value of <math>x_i</math>
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| In [[set theory]] and some [[electrical engineering]] contexts, [[negation]] operators can be written as an overline above the term or expression to be negated, for example:
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| :Common set theory notation:
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| ::<math>\overline{A \cap B}=\overline{A} \cup \overline{B} \iff \overline{A \cup
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| B}=\overline{A} \cap \overline{B}</math>
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| :Electrical engineering notation illustrating [[De Morgan's Laws]] with the saying, "break the line, change the sign":
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| ::<math>\overline{A + B}=\overline{A} \cdot \overline{B} \iff \overline{A \cdot B}=\overline{A} + \overline{B} \iff \overline{AB}=\overline{A} + \overline{B} \iff \overline{A + B}</math>
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| :in which implied multiplication, the times (cross) and the dot all mean logical AND, and the plus sign means logical OR.
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| In the repetition and negation usages, this notation is also referred to as a [[vinculum (symbol)|vinculum]].
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| The overline notation can indicate a [[complex conjugate]] and analogous operations.
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| *if <math>x = a + ib</math>, then <math>\overline{x} = a - ib.</math>
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| In physics, an overline sometimes indicates a [[Euclidean vector|vector]], although boldface and arrows are also commonly used:
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| * <math>\overline x=|x|\hat x</math>
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| In [[crystallography]], an overline indicates an [[improper rotation]] or a [[negative number]]:
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| * <math>\overline 3</math> is the [[Hermann–Mauguin notation]] for a threefold rotoinversion.
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| * <math>[\overline 11\overline2]</math> is the direction with [[Miller index|Miller indices]] <math>h=-1</math>, <math>k=1</math>, <math>l=-2</math>.
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| ==Linguistics==
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| [[X-bar theory]] makes use of overbar notation to indicate differing levels of [[syntactic structure]]. Certain structures are represented by adding an overbar to the unit, as in {{overline|X}}. Due to difficulty in typesetting the overbar, the [[prime symbol]] is often used instead, as in X′. Contemporary typesetting software such as [[LaTeX]] has made typesetting overbars considerably simpler; both prime and overbar markers are accepted usages. Some variants of X-bar notation use a double-bar (or double-prime) to represent phrasal-level units.
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| X-bar theory derives its name from the overbar. One of the core proposals of the theory was the creation of an intermediate syntactic node between phrasal (XP) and unit (X) levels; rather than introduce a different label, the intermediate unit was marked with a bar.
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| ==Technical notes==
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| * In [[HTML]] using [[Cascading Style Sheets|CSS]], <code><nowiki><span style="text-decoration: overline">text</span></nowiki></code>, results in: {{overline|text}}
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| * In HTML documents, the macron can be produced with <code>&#x304;</code> ([[decimal]] <code>&#772;</code>), and the "combining overline" — with <code>&#x305;</code> (<code>&#773;</code>).
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| * In [[TeX]], a single symbol can be overlined with <code>\bar x</code> or <code>\bar{x}</code>. Longer sections can be overlined with <code>\overline{ABC}</code>, where a space is written as "<code>\ </code>" and an [[Umlaut diacritic|umlaut]] is written as "<code>\ddot a</code>".
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| * In [[Microsoft Windows]], the [[ISO/IEC 8859-1]] 0xAF symbol mentioned above can be added in any program with the keystrokes Alt+0175 (where numbers are entered from the [[numeric keypad]]).
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| * In [[GTK+|GTK]]/GTK+, the symbol can be added using the keystrokes Ctrl+Shift+U to activate [[Unicode input]], then type "00AF" as the code for the character.
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| * In [[Microsoft Word]], overstriking of text can be accomplished with the <code>EQ \O()</code> field code. The field code <code>{EQ \O(x,¯)}</code> produces {{overline|x}} and the field code <code>{EQ \O(xyz,¯¯¯)}</code> produces {{overline|xyz}}.
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| * [[LibreOffice]] has direct support for several styles of overline in its "Format / Character / Font Effects" dialog.
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| Overstriking of longer sections of text, such as in {{overline|123}}, can also be produced in many [[Word processing|text processors]] as [[markup language|text markup]] as a special form of understriking.
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| == References ==
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| <references>
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| <ref name="UnicodeFull">{{Citation
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| | chapter-url = http://www.unicode.org/charts/PDF/UFF00.pdf
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| | chapter =Halfwidth and Fullwidth Forms
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| | title = The Unicode Standard 6.1
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| | author = The Unicode Consortium
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| | year= 2012
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| | isbn = 978-1-936213-02-3
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| | quote = FULLWIDTH MACRON • sometimes treated as fullwidth overline
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| }}</ref>
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| </references>
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| == See also ==
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| * [[Underscore]]
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| * [[Strikethrough]]
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| * [[Underline]]
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| {{iw-ref|de|Überstrich|January 15, 2008}}
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| [[Category:Typography]]
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| [[Category:Punctuation]]
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