puppet include vs require vs contain

contain.pp

class ntp {
  file { '/etc/ntp.conf':
    ...
    require => Package['ntp'],
    notify  => Class['ntp::service'],
  }
  contain ntp::service
}

class main {
  include ntp
  # this exec will run strictly after Class['ntp'] but not neccesarily after Class['ntp::service']
  # just like if all resources from Class['ntp::service'] are declared in Class['ntp']
  # AKA (something like)
  # Class['ntp'] -> Exec['/bin/runme.sh']
  # Class['ntp::service'] -> Exec['/bin/runme.sh']
  exec { '/bin/runme.sh':
    require => Class['ntp'],
  }
}

include-require.pp

class ntp {
  file { '/etc/ntp.conf':
    ...
    require => Package['ntp'],
    notify  => Class['ntp::service'],
  }
  include ntp::service
  package { 'ntp':
    ...
  }
}

class main {
  include ntp
  # this exec will run strictly after Class['ntp'] and all resources in it, but not necessarily after Class['ntp::service']
  # AKA
  # Class['ntp'] -> Exec['/bin/runme.sh']
  # but there will be no dependency like this one:
  # Class['ntp::service'] -> Exec['/bin/runme.sh']
  exec { '/bin/runme.sh':
    require => Class['ntp'],
  }
}

include.pp

class ntp {
  file { '/etc/ntp.conf':
    ...
    require => Package['ntp'],
    notify  => Class['ntp::service'],
  }
  include ntp::service
}

class main {
  include ntp
  # this exec will run randomly, without any dependencies with any class from above
  exec { '/bin/runme.sh':
  }
}