initRangeSet = (name, range) => {
    mediaRanges.set(name, range);
  }
Initializes a screen width media query range set.

This initialization step makes the range set ready to be used for one of the other functions in namespace <code>MediaRange</code>.

A range set can be defined as shown in the following example:
<pre>
MediaRange.initRangeSet("MyRangeSet", [200, 400], ["Small", "Medium", "Large"]);
</pre>
This example defines the following named ranges:
<ul>
<li><code>"Small"</code>: For screens smaller than 200 pixels.</li>
<li><code>"Medium"</code>: For screens greater than or equal to 200 pixels and smaller than 400 pixels.</li>
<li><code>"Large"</code>: For screens greater than or equal to 400 pixels.</li>
</ul>

@param {string} name The name of the range set to be initialized.
The name must be a valid id and consist only of letters and numeric digits.
@param {Range} [range] The given range set.
@name MediaRange.initRangeSet