function SLen(VAR s: packed array [slow..shigh: integer] of char
  	):integer
  	;
   EXTERNAL;
{*USER*
 
The SLEN function the length of string "S". If S is a type0 string,
the length is ORD(s[0]).  If S is a type1 string, then the length is
computed from the S[1] to the last non-null character in the S array.
 
An invalid string (neither type0 or type1) will be ignored, and the
length returned as zero.  In addition, a type0 string whose length
byte (byte 0) is greater than the upper subscript of the array, will
be considered invalid, ignored, and the length returned as zero.
 
To aid in debugging, a non-fatal error message
will be issued when an invalid string is encountered.
For this reason, SLEN is a quick way to check that
an array is a type0 or type1 string.  Note that no validation status
is returned to the caller, but the error message to the terminal will
advise programmer of a program bug.
 
}