If there is only _one_ element that will match `.picker-container`, then it should really have an id and be found in the DOM with `document.getElementById`—which is significantly more performant then `document.querySelector`. If additional markup is undesirable, then I'd recommend caching the `<div id="time-picker">` element and reusing it as context through-out the codebase:

```js
var context = document.getElementById('time-picker');

// ... later...
this._containers.time = context.querySelector('.picker-container'); // limits the query to the tree below <div id="time-picker">

// ...even later...
pickerElements.forEach(function(className) {
  context.querySelector(className).addEventListener('mousedown', this);
}, this);
```