feat(select): improve accessibility

src/lib/select/select-errors.ts

@@ -0,0 +1,18 @@
+/**
+ * Returns an exception to be thrown when attempting to assign a non-array value to a select
+ * in `multiple` mode. Note that `undefined` and `null` are still valid values to allow for
+ * resetting the value.
+ * @docs-private
+ */
+export function getLySelectNonArrayValueError(): Error {
+  return Error('Value must be an array in multiple-selection mode.');
+}
+
+/**
+ * Returns an exception to be thrown when assigning a non-function value to the comparator
+ * used to determine if a value corresponds to an option. Note that whether the function
+ * actually takes two values and returns a boolean is not checked.
+ */
+export function getLySelectNonFunctionValueError(): Error {
+  return Error('`compareWith` must be a function.');
+}

src/lib/select/select.html

@@ -7,7 +7,16 @@
 </div>
 
 <ng-template #templateRef>
-  <div #container [className]="classes.container" [@selectEnter]="'in'" (@selectLeave.done)="_endAnimation($event)">
+  <div
+    #container
+    tabindex="-1"
+    role="listbox"
+    [className]="classes.container"
+    [@selectEnter]="'in'"
+    (@selectEnter.done)="_panelDoneAnimatingStream.next($event.toState)"
+    (keydown)="_handleKeydown($event)"
+    [style.font-size.px]="_triggerFontSize"
+  >
     <ng-content></ng-content>
   </div>
 </ng-template>