Built-In Functions

In this section, several of the function arguments are named with the
following conventions:

 "number"   must be numeric.
 "length"   must be a non-negative whole number.
 "count"    must be a non-negative whole number.
 "position" must be a positive whole number.
 "pad"      must be a string of length 1.
 "option"   must be a nonempty string.  Only the first character of the
            option is significant, and it is translated to uppercase
            before use.
 "file"     must be the name of a stream.  This can be any nonempty
            string which does not contain NUL characters ('0'x).