the colon is quite often used as a special control character in many operating systems commands, urls, computer programming languages, and in the path representation of several file systems. it is often used as a single post-fix delimiter, signifying the immediate precedence of a token keyword or the transition from one mode of character string interpretation to another related mode. some applications, such as the widely used mediawiki, use the colon as both a pre-fix and post-fix delimiter.