Start experiment: associate key bindings with CSS selectors

KeyEventHandler holds references to BindingSets. The name "binding set"
is based on the concept of a CSS ruleset. The idea is to choose a key
binding for an event based on what selectors (match / most closely
contain) the event's target DOM node.

src/atom/binding-set.coffee

@@ -0,0 +1,46 @@
+$ = require 'jquery'
+
+module.exports =
+class BindingSet
+  namedKeys:
+    backspace: 8, tab: 9, clear: 12, enter: 13, 'return': 13,
+    esc: 27, escape: 27, space: 32, left: 37, up: 38, right: 39,
+    down: 40, del: 46, 'delete': 46, home: 36, end: 35, pageup: 33,
+    pagedown: 34, ',': 188, '.': 190, '/': 191, '`': 192, '-': 189,
+    '=': 187, ';': 186, '\'': 222, '[': 219, ']': 221, '\\': 220
+
+  selector: null
+  bindings: null
+
+  constructor: (@selector, @bindings) ->
+
+  commandForEvent: (event) ->
+    if $(event.target).is(@selector)
+      for pattern, command of @bindings
+        return command if @eventMatchesPattern(event, pattern)
+    null
+
+  eventMatchesPattern: (event, pattern) ->
+    pattern = @parseKeyPattern pattern
+    pattern.ctrlKey == event.ctrlKey and
+      pattern.altKey == event.altKey and
+      pattern.shiftKey == event.shiftKey and
+      pattern.metaKey == event.metaKey and
+      pattern.which == event.which
+
+  parseKeyPattern: (pattern) ->
+    [modifiers..., key] = pattern.split '+'
+
+    if @namedKeys[key]
+      charCode = @namedKeys[key]
+      key = null
+    else
+      charCode = key.toUpperCase().charCodeAt 0
+
+    ctrlKey: 'ctrl' in modifiers
+    altKey: 'alt' in modifiers
+    shiftKey: 'shift' in modifiers
+    metaKey: 'meta' in modifiers
+    which: charCode
+    key: key
+

src/atom/key-event-handler.coffee

@@ -0,0 +1,19 @@
+$ = require 'jquery'
+BindingSet = require 'binding-set'
+
+module.exports =
+class KeyEventHandler
+  bindingSetsBySelector: null
+
+  constructor: ->
+    @bindingSets = []
+
+  bindKeys: (selector, bindings) ->
+    @bindingSets.push(new BindingSet(selector, bindings))
+
+  handleKeypress: (event) ->
+    for bindingSet in @bindingSets
+      if command = bindingSet.commandForEvent(event)
+        $(event.target).trigger(command)
+        return
+