This function has two signatures:
Returns a new string that is a substring of the original text string. It begins with the character at the specified index and extends to the end of text string.
Returns a new string that is a substring of the original text string. The substring begins at the specified startOffset and extends to the character at index endOffset - 1.
substring('abcd', 1) returns the string 'bcd'.
substring('abcd', 4) returns an empty string.
substring('abcd', 1, 3) returns the string 'bc'.