Summary:
Extraction of a part of a string.

Syntax:
substring(string-expr, begin-index, end-index)

Description:
Returns the substring of the string returned by string-expr , begining at the position (counted from 0) corresponding to the evaluation of begin-index and extending to the character at index corresponding at the evaluation of end-index - 1. Thus the length of the substring is end-index - begin-index. If string-expr does not evaluate to a string, or if begin-index or end-index does not evaluate to an integer, or if  begin-index < 0, or if end-index > length(expr₁), an error is returned.

Example:

variable: birthYear
  type: string
  definition: birthYear = right(socialSecurityCode, 1, 2)

left, right, length