hi,

checker on http://validator.w3.org/check says:

 Line 289, Column 92: The for attribute of the label element must refer to a form control.
…lass="left" for="Form_LeadForm_Gender">Anrede</label><div class="middleColumn"…

and here the field or SS generated HTML code

<div id="Gender" class="field optionset "><label class="left" for="Form_LeadForm_Gender">Anrede</label><div class="middleColumn"><ul id="Form_LeadForm_Gender" class="optionset ">
<li class="odd valm"><input id="Form_LeadForm_Gender_m" name="Gender" type="radio" value="m"  class="radio" /> <label for="Form_LeadForm_Gender_m">Herr</label></li>
<li class="even valf"><input id="Form_LeadForm_Gender_f" name="Gender" type="radio" value="f"  class="radio" /> <label for="Form_LeadForm_Gender_f">Frau</label></li>
</ul>
</div></div>

the validation passes with

for="Form_LeadForm_Gender_m"

or

for="Form_LeadForm_Gender_f"

Good catch. The label in that case shouldn't have a for attribute. Submit it as a bug on open.silverstripe.org. I'm not sure how that'd be fixed (the label comes from the parent form holder) but we may need to introduce a new for attribute which is not set on Optionsetfields.

ok, done: http://open.silverstripe.org/ticket/7162