Straight single and double quotation marks are used in most programming languages to delimit strings or literal characters, collectively known as string literals. In some languages (e.g. Pascal) only one type is allowed, in some (e.g. C and its derivatives) both are used with different meanings and in others (e.g. Python) both are used interchangeably. In some languages, if it is desired to include the same quotation marks used to delimit a string inside the string, the quotation marks are doubled. For example, to represent the string in Pascal one uses codice_3. Other languages use an escape character, often the backslash, as in codice_4.