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<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="../iron-a11y-keys-behavior/iron-a11y-keys-behavior.html">


<script>

/*
`iron-a11y-keys` provides a normalized interface for processing keyboard commands that pertain to [WAI-ARIA best
practices](http://www.w3.org/TR/wai-aria-practices/#kbd_general_binding). The element takes care of browser differences
with respect to Keyboard events and uses an expressive syntax to filter key presses.

Use the `keys` attribute to express what combination of keys will trigger the event to fire.

Use the `target` attribute to set up event handlers on a specific node.
The `keys-pressed` event will fire when one of the key combinations set with the `keys` attribute is pressed.

Example:

This element will call `arrowHandler` on all arrow keys:

    <iron-a11y-keys target="{{}}" keys="up down left right" on-keys-pressed="{{arrowHandler}}"></iron-a11y-keys>

Keys Syntax:

The `keys` attribute can accepts a space seprated, `+` concatenated set of modifier keys and some common keyboard keys.

The common keys are `a-z`, `0-9` (top row and number pad), `*` (shift 8 and number pad), `F1-F12`, `Page Up`, `Page
Down`, `Left Arrow`, `Right Arrow`, `Down Arrow`, `Up Arrow`, `Home`, `End`, `Escape`, `Space`, `Tab`, and `Enter` keys.

The modifier keys are `Shift`, `Control`, and `Alt`.

All keys are expected to be lowercase and shortened:
`Left Arrow` is `left`, `Page Down` is `pagedown`, `Control` is `ctrl`, `F1` is `f1`, `Escape` is `esc` etc.

Keys Syntax Example:

Given the `keys` attribute value "ctrl+shift+f7 up pagedown esc space alt+m", the `<iron-a11y-keys>` element will send
the `keys-pressed` event if any of the follow key combos are pressed: Control and Shift and F7 keys, Up Arrow key, Page
Down key, Escape key, Space key, Alt and M key.

Slider Example:

The following is an example of the set of keys that fulfil the WAI-ARIA "slider" role [best
practices](http://www.w3.org/TR/wai-aria-practices/#slider):

    <iron-a11y-keys target="{{}}" keys="left pagedown down" on-keys-pressed="{{decrement}}"></iron-a11y-keys>
    <iron-a11y-keys target="{{}}" keys="right pageup up" on-keys-pressed="{{increment}}"></iron-a11y-keys>
    <iron-a11y-keys target="{{}}" keys="home" on-keys-pressed="{{setMin}}"></iron-a11y-keys>
    <iron-a11y-keys target="{{}}" keys="end" on-keys-pressed="{{setMax}}"></iron-a11y-keys>

The `increment` function will move the slider a set amount toward the maximum value.
The `decrement` function will move the slider a set amount toward the minimum value.
The `setMin` function will move the slider to the minimum value.
The `setMax` function will move the slider to the maximum value.

Keys Syntax Grammar:

[EBNF](http://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_Form) Grammar of the `keys` attribute.

    modifier = "shift" | "ctrl" | "alt";
    ascii = ? /[a-z0-9]/ ? ;
    fnkey = ? f1 through f12 ? ;
    arrow = "up" | "down" | "left" | "right" ;
    key = "tab" | "esc" | "space" | "*" | "pageup" | "pagedown" | "home" | "end" | arrow | ascii | fnkey ;
    keycombo = { modifier, "+" }, key ;
    keys = keycombo, { " ", keycombo } ;

@demo demo/index.html
*/


  Polymer({
    is: 'iron-a11y-keys',

    behaviors: [
      Polymer.IronA11yKeysBehavior
    ],

    properties: {
      /** @type {?Node} */
      target: {
        type: Object,
        observer: '_targetChanged'
      },

      keys: {
        type: String,
        reflectToAttribute: true,
        observer: '_keysChanged'
      }
    },

    attached: function() {
      if (!this.target) {
        this.target = this.parentNode;
      }
    },

    _targetChanged: function(target) {
      this.keyEventTarget = target;
    },

    _keysChanged: function() {
      this.removeOwnKeyBindings();
      this.addOwnKeyBinding(this.keys, '_fireKeysPressed');
    },

    _fireKeysPressed: function(event) {
      this.fire('keys-pressed', event.detail, {});
    }
  });
</script>