|  |  4.21.4 string operations 
 
+concatenation
<=,>=,==,<>comparison (lexicographical with respect to the ASCII encoding)
string_expression [int_expression]is a character of the string; the index 1 gives the first character.
string_expression [int_expression,int_expression]is a substring, where the first argument is the start index and the
second is the length of the substring, filled up with blanks if the
length exceeds the total size of the string
string_expression [intvec_expression]is a expression list of characters from the string
 
Example:
 |  |   string s="abcde";
  s[2];
==> b
  s[3,2];
==> cd
  ">>"+s[1,10]+"<<";
==> >>abcde     <<
  s[2]="BC"; s;
==> aBcde
  intvec v=1,3,5;
  s=s[v]; s;
==> ace
  s="654321"; s=s[3..5]; s;
==> 432
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