Semantics : PrintArgument
This is a value to be printed, optionally with text alignment formatting
and repeating. The repeating is specified by { } or repeat clause,
which are the same.
The :< , :> and :* decorators are for left-, right- and
center-alignment, with the following value as the width. If the value is
followed by a ! , the width is forced with possible truncations. If the
value of width has a decimal point, then the part on either side is the
width for the respective part of a floating-point number.