title: Elm check whether ctrl key pressed onClick
body: <p>Using elm-html, how can I check whether the ctrl key is pressed at the time of the click?</p>
  
  <p>Is "control key down" some state I'd need to maintain elsewhere, perhaps using the Keyboard module? If so, how would that fit into elm-html?</p>
  
  <p>I've adapted the code below from one of the well-known elm examples:</p>
  
  <pre><code>import Keyboard
  import Html exposing (..)
  import Html.Attributes exposing (style)
  import Html.Events exposing (onClick)
  import Signal exposing(Signal, Mailbox)
  
  
  type alias Model =
    { count: Int
    , ctrl : Bool
  }
  
  initialModel : Model
  initialModel = { count = 0, ctrl = False}
  
  type Action = Increment | Decrement | NoOp
  
  update : Action -&gt; Model -&gt; Model
  update action model =
    case action of
      Increment -&gt;
        { model | count = model.count + 1 }
      Decrement -&gt;
        { model | count = model.count - 1 }
      NoOp -&gt;
        model
  
  
  view : Signal.Address Action -&gt; Model -&gt; Html
  view address model =
    div []
      [ button [ onClick address Decrement ] [ text "-" ]
      , div [] [ text (toString model) ]
      , button [ onClick address Increment ] [ text "+" ]
      ]
  
  
  actions : Mailbox Action
  actions =
    Signal.mailbox NoOp
  
  model : Signal Model
  model =
    Signal.foldp update initialModel actions.signal -- Keyboard.ctrl ?
  
  main =
    Signal.map (view actions.address) model
  </code></pre>
  
  <p>How can I update the value of the model's "ctrl" field?</p>