Double hyphen
In Latin script, the double hyphen is a punctuation mark that consists of two parallel hyphens. It was a development of the earlier which developed from a Central European variant of the virgule slash, originally a form of scratch comma. Similar marks (see below) are used in other scripts. In order to avoid it being confused with the equals sign , the double hyphen is often given as double oblique hyphen in modern typography. The double hyphen is also not to be confused with two consecutive hyphens (--), which are often used to represent an em dash or en dash  ; that practice arose due to the limitations of typewriter character sets which did not have both hyphen and dash. Usage. The double hyphen is used for several different purposes throughout the world: Stylistic variant of the single hyphen. When the double hyphen is used as a functionally equivalent graphical variant (allograph) of the single hyphen, it has the same Unicode code point as a conventional hyphen (since how it is displayed/printed is a font choice on that occasion). Similar marks. Other forms of double hyphen are given unique codepoints in Unicode: