Strikethrough

Strikethrough is a typographical presentation of words with a horizontal line through their center, resulting in text like this. Contrary to censored or sanitized (redacted) texts, the words remain readable. This presentation signifies one of two meanings. In ink-written, typewritten, or other non-erasable text, the words are a mistake and not meant for inclusion. When used on a computer screen, however, it indicates deleted information. It can also be used deliberately to imply a change of thought (as in epanorthosis).

Uses

Marking errors

Strikethrough is primarily used to mark text that is mistaken or to be removed. Historically, this has also been marked by placing dots under the letters to be ignored (Latin: punctum delens).[1]

Physics
Main article: Feynman slash notation

In quantum field theory, a slash through a symbol, such as ⱥ, is shorthand for γμaμ, where a is a covariant four-vector, the γμ are the gamma matrices, and the repeated index μ is summed over according to the Einstein notation.

Highlighting

In medieval manuscripts such as the Domesday Book, "strikethrough" of text with red ink often functions as highlighting similar to modern underline.[2]

Computer representations

HTML

The HTML presentational inline element for strikethrough is <strike> or <s> This element was, however, deprecated in the 1999 HTML 4.01 standard, and replaced by the <del> tag, a semantic element representing deleted text, which user agents (typically web browsers) often render as a strikethrough.[3][4]

In the HTML5 draft, there is no presentational element for strikethrough. However, there are two related semantic elements. Firstly, <s>, that is strikethrough in HTML 3 and 4, is redefined to mark text that is no longer correct, and secondly, <del> marks text that has been deleted, as it does in HTML 4.01.[5][6]

Other markup symbols
  • BB Code is a markup language used on many web forums. The BB Code for strikethrough is [s] or [strike].
  • GitHub flavored Markdown uses double tilde ~~ to wrap around text for strikethrough.[7]
  • Gmail chat uses minus sign - to wrap around text for strikethrough.[8]

CSS

In cascading style sheets (CSS) strikethrough is controlled using the text-decoration property, and specified by the line-through value of that property. For example, <span style="text-decoration: line-through;">ABCD efghi</span> renders like this: ABCD efghi

To maintain backwards compatibility, the following can be added to the CSS: strike {text-decoration:line-through;} The example above could then be written like this: <strike>ABCD efghi</strike>, which is compatible with HTML 4. In HTML 5, this: <del>ABCD efghi</del> also produces the same result, although the use of CSS is preferred and the del tag carries a semantic interpretation not present in the purely stylistic s and strike tags.

Combining characters

In plain text scenarios where markup cannot be used, Unicode offers a number of combining characters that achieve similar effects.

The “combining long stroke overlay” (U+0336) results in an unbroken stroke across the text:

  • A̶B̶C̶D̶ ̶e̶f̶g̶h̶i̶

while the “combining short stroke overlay” (U+0335) results in individually struck out characters:

  • A̵B̵C̵D̵ ̵e̵f̵g̵h̵i̵

Similarly, the “combining short solidus overlay” (U+0337) results in diagonally struck out letters:

  • A̷B̷C̷D̷ ̷e̷f̷g̷h̷i̷

as does the “combining long solidus overlay” (U+0338), which produces longer diagonal strokes:

  • A̸B̸C̸D̸ ̸e̸f̸g̸h̸i̸

Specific struck-through characters

A number of characters that have the visual appearance of struck-through characters exist in Unicode, including ƀ, Đđ, Ǥǥ, Ħħ, Ɨɨ, Ɉɉ, Łł, Ɵɵ, Ŧ, ʉ, Ƶƶ, ƻ, ʡ, ʢ, Ғғ, Ҟҟ, Ұұ, Ҍҍ. These usually have specific functions (for example, in the Latin Extended-A character set) or representations and are not intended for general use. However, they are not precomposed characters and have neither canonical nor compatibility decompositions. This issue has created security considerations since "precomposed" characters like U+019F and sequences like U+004F U+0335 or U+004F U+0336 often cause visual confusion (compare Ɵ and O̵ and O̶). Unicode has acknowledged this issue and has proposed a standardized method for counteraction.[9][10]

Double/multiple strikethrough

Double strikethrough is an option in certain word processing applications such as Microsoft Word. There is no generally agreed meaning of double strikethrough, but it may be used as a second level of single strikethrough.

In Japan, double strikethrough is conventionally used (rather than single strikethrough) when striking out text. This is for added clarity, as in complex kanji a single strikethrough may be missed or confused with a stroke in the character.

Double, triple or multiple strikethrough may also (especially formerly) be used as a way of emphasising words.

Research

Since at least 2014, researchers in the area of optical character recognition have attempted to solve the problem of recognizing struck-out text in handwritten documents.[11][12]

See also

References
  1. Hackett, M.B. (1970). The original statutes of Cambridge University : the text and its history (Digitally printed version, re-issue. ed.). Cambridge: Cambridge Eng. University Press. p. 185. ISBN 9780521070768.
  2. See, e.g., this image from the British National Archives' Focus on the Domesday Book.
  3. 15.2.1 Font style elements: the TT, I, B, BIG, SMALL, STRIKE, S, and U elements, HTML 4.01 Specification: Alignment, font styles, and horizontal rules, W3C. 24 December 1999.
  4. 9.4 Marking document changes: The INS and DEL elements HTML 4.01 Specification: Text – Paragraphs, Lines, and Phrases, W3C. 24 December 1999.
  5. 4.5.5 The s element Archived 2015-08-01 at the Wayback Machine HTML5, W3C Last Call Working Draft. 17 June 2014.
  6. 4.6.2 The del element HTML5, W3C Last Call Working Draft 17 June 2014
  7. "GitHub Flavored Markdown".
  8. "Formatting text with-Google bold italic strikethrough". (subscription required)
  9. The Unicode Consortium, The Unicode Standard, Chapter 2, Page 44, Non-decomposition of Overlaid Diacritics
  10. The Unicode Consortium, Unicode Technical Standard #39: Unicode Security Mechanisms, chapter Confusable Detection
  11. Adak, Chandranath; Chaudhuri, Bidyut B. (2014). "An Approach of Strike-Through Text Identification from Handwritten Documents". 2014 14th International Conference on Frontiers in Handwriting Recognition. pp. 643–648. doi:10.1109/ICFHR.2014.113. ISBN 978-1-4799-4334-0.
  12. Chaudhuri, Bidyut B.; Adak, Chandranath (2017). "An approach for detecting and cleaning of struck-out handwritten text". Pattern Recognition. 61: 282–294. doi:10.1016/j.patcog.2016.07.032.
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