Underscore
In proofreading, underscoring is a convention that says "set this text in italic type", traditionally used on manuscript or typescript as an instruction to the printer.
In modern usage, underscoring is achieved with a markup language, with the Unicode combining low line or as a standard facility of word processing software.
The free-standing underscore character is used to indicate word boundaries in situations where spaces are not allowed, such as in computer filenames, email addresses, and in Internet URLs, for example Mr_John_Smith.
[2][a] In a manuscript (or typescript) to be typeset, various forms of underlining (see below) were therefore conventionally used to indicate that text should be set in special type such as italics, part of a procedure known as markup.
In printed documents underlining is generally avoided, with italics or small caps often used instead, or (especially in headings) using capitalization, bold type or greater body height (font size).
In German, Slovene and some other Slavic languages, the underscore has recently gained prominence as the punctuation to form gender-neutral suffixes in gendered nouns and other parts of the speech.
In mathematical notations, underscores are sometimes used in the following contexts: In web browsers, default settings typically distinguish hyperlinks by underlining them (and usually changing their color), but both users and websites can change the settings to make some or all hyperlinks appear differently (or even without distinction from normal text).
This convention is known as "snake case" (the other popular method is called camelCase, where capital letters are used to show where the words start).
[12] In HTML5, the tag reappeared but its meaning was changed significantly: it now "represents a span of inline text which should be rendered in a way that indicates that it has a non-textual annotation".
The Text Encoding Initiative (TEI) provides an extensive selection of related elements for marking editorial activity (insertion, deletion, correction, addition, etc.).
Unicode has a free-standing underscore _ at U+005F, inherited from ASCII, which is a legacy of the typewriter practice of underlining using backspace and overtype.
