form.php
protected function addRadioButton($tag)
    {
        if (! isset($this->radios[$tag->getName()])) {
            $this->widgets[]               = new SimpleRadioGroup();
            $this->radios[$tag->getName()] = count($this->widgets) - 1;
        }
        $this->widgets[$this->radios[$tag->getName()]]->addWidget($tag);
    }
protected function addRadioButton($tag)
    {
        if (! isset($this->radios[$tag->getName()])) {
            $this->widgets[]               = new SimpleRadioGroup();
            $this->radios[$tag->getName()] = count($this->widgets) - 1;
        }
        $this->widgets[$this->radios[$tag->getName()]]->addWidget($tag);
    }
Adds a radio button, building a group if necessary.

@param SimpleRadioButtonTag $tag   Incoming form control.