Assuming you have read the basics for inputfields and their naming, the same rules apply for radio buttons.
Radio buttons with the same name will be automatically grouped by your browser. So that is pretty basic stuff.
A difference is found in the way the form remembers the previous setting (after a rejected submit).
The previous selected input field will need to have "checked="checked" to reactivate the previous choice.
To do that we can use the fieldname + value as "remember" field. Set in uppercase, linked with an underscore and between curly brackets it looks like the two lines below.
<input type="radio" {TITLE_MR} id="t1" name="mf_r_title" value="Mr"><label for="t1">Mr.</label> <input type="radio" {TITLE_MRS} id="t2" name="mf_r_title" value="Mrs"><label for="t2">Mrs.</label>
Since styling radio-buttons is not easy to do a error class is best set on a surrounding <div>.
You can look in the included "form_EN_full_contactform.htt " how this is done:
<div class="grouping {TITLE_ERROR}"> <input type="radio" {TITLE_MR} id="t1" name="mf_r_title" value="Mr"><label for="t1">Mr.</label> <input type="radio" {TITLE_MRS} id="t2" name="mf_r_title" value="Mrs"><label for="t2">Mrs.</label> </div>
In previous versions of the miniform you would need to use a hidden field if the field was a required field.
In version 0.4 and later this is not needed anymore!