@SUBSTR[string,start,length] : An older version of @INSTR. If the length is omitted, it will default to the remainder of string. If string includes commas, it must be quoted with double quotes ["] or back-quotes [`], or each comma must be preceded by an Escape character The quotes count in calculating the position of the substring. @INSTR, which has string as its last parameter, does not have this restriction.
Numeric input may be entered in either decimal format (a sequence of 0-9 digits) or in hexadecimal format ("0x" followed by a sequence of 0-F hex digits).
echo %@substr[this is useful,8]
echo %@substr[this is useful,8,-2]
echo %@substr["commas, they DO matter",9]
they DO matter"
echo %@substr[commas^, they DO matter,9]
they DO matter
See also: @INSTR.