The first form steps through the sequence from
identifying characters that are part of a format sequence.
Each character that is not part of a format sequence is written to
immediately, and each format sequence, as it is identified, results in
a call to
thus, format elements and other characters are interleaved in the output
in the order in which they appear in the pattern.
Format sequences are identified by converting each character
value as if by
is a reference to
The first character of each sequence is equal to
followed by an optional modifier character
and a format specifier character
as defined for the function
If no modifier character is present,
For each valid format sequence identified, calls
do_put(s, str, fill, t, spec, mod).