Returns the seconds component of an xs:time.
fn:seconds-from-time( $arg as xs:time?xs:decimal?If $arg is the empty sequence, the function returns the empty sequence.
Otherwise, the function returns an xs:decimal value greater than or equal
to zero and less than 60, representing the seconds and fractional seconds in the local
value of $arg.
The expression fn:seconds-from-time(xs:time("13:20:10.5")) returns 10.5.