The STR function will convert arg to a string. If arg is a number, the result will be the ASCII equivalent to the number. If arg is a label, the result will be a string that contains the name of the label. If arg is an assembler variable then the STR function is applied to the value of the variable. If STR is used without an argument it will produce an empty string. This is important since the argument to STR may be a macro parameter which gets expanded to nothing. This would be the same as using STR without an argument.