What is controlling the radio buttons in HTML5

Question

Take this code for Example

<form>
<input type="radio" name="sex" value="male" checked>Male
<br>
<input type="radio" name="sex" value="female">Female
</form>

It allows a user to select one button at a time, I was always under the impression that javascript was the answer to this type of a solution. So my question is, is there any embedded javascript in the HTML radio button and if not, where is the function coming from?

Answer 1

Its the Browser's duty to do that for us.

Why?

Because the behavior is stated in the spec:

http://www.w3.org/TR/html/forms.html#radio-button-state-(type=radio)