Strings are used in WRITE statements, in other output statements (such as error messages), and to name files. A string consists of any number of characters enclosed in double quotes. For example:
Lower case characters within a string are not converted to upper case.
The string ~~ represents the empty string. A double quote may be included in a string by preceding it by another double quote. Thus ~a~~b~ is the string a~b, and ~~~~ is the string consisting of the single character ~.