(single-byte) character used by functions that convert between a (single-byte)
character sequence and a value of one of the floating-point types.
It is used
in the character sequence to denote the beginning of a fractional part.
represented in [support] through [thread]
and [depr] by a period,
also its value in the "C"
locale, but may change during program
execution by a call to
or by a change to a
object, as described in [locales] and [input.output].