Related "checkbox" input fields should be grouped together using a fieldset

Example

Wrong

<input type="checkbox" name="option-a" id="a"/><label for="a">Option A</label><br/><input type="checkbox" name="option-b" id="b"/><label for="b">Option B</label>

Right

<fieldset><legend>Several options</legend><input type="checkbox" name="option-a" id="a"/><label for="a">Option A</label><br/><input type="checkbox" name="option-b" id="b"/><label for="b">Option B</label></fieldset>