'apple'                true
'apple banana'         true
'apple banana orange'  true
' apple banana'        true
'  apple banana'       true
' '                    false
'  '                   false
'   '                  false

^(?!s+$).+

^         # start of the line / string
(?!s+$)  # neg. lookahead, making sure there are not only whitespaces
.+        # at least one character, possibly more

^s*S.*$

^(?=.*S).*

^(?=.*S)(?!.*d).*

S