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            Returns
a substring of a given string. The substring is specified by the
index of the given string where the substring begins and the length
of the substring. The length can be specified either explicitly
or as the remaining characters after the beginning of the substring.
            
            
             
            
            
             Syntax
                substring(string, number, number?) 
            
             
            
            
             Parameters
            
             A
string and one or more numbers separated by commas. The string is
the parameter from which
             
              the
             
             substring is extracted.
The first number is the index of the string parameter where the
substring begins. The second number, if provided, is the length
of the substring. If the third parameter is not provided, the substring
includes the characters from the index to the end of the given string.
             
            
             
            
            
             Example
            
             For
example, the first of the following two expressions returns
             
              234
             
             ,
and the second expression returns
             
              6789
             
             :
             substring("123456789",2,3) 
substring("123456789",6) 
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