A whitespace character is one that the interpreter recognizes as a "blank" or "space" character. There are two characters used by Rexx as whitespace that can be used interchangeably:

Horizontal tabs encountered in Rexx program source are converted into blanks, allowing tab characters and blanks to be use interchangeably in source. Additionally, Rexx operations such as the PARSE instruction or the SUBWORD() built-in function will also accept either blank or tab characters as word delimiters.