Method getFieldAttribute

/**
 * Method to get an attribute value from a field XML element.  If the attribute doesn't exist or
 * is null then the optional default value will be used.
 *
 * @param   string  $name       The name of the form field for which to get the attribute value.
 * @param   string  $attribute  The name of the attribute for which to get a value.
 * @param   mixed   $default    The optional default value to use if no attribute value exists.
 * @param   string  $group      The optional dot-separated form group path on which to find the field.
 *
 * @return  mixed  The attribute value for the field.
 *
 * @since   1.7.0
 * @throws  \UnexpectedValueException
 */
public function getFieldAttribute($name, $attribute, $default = null, $group = null)
{
    // Make sure there is a valid Form XML document.
    if (!$this->xml instanceof \SimpleXMLElement) {
        throw new \UnexpectedValueException(sprintf('%s::%s `xml` is not an instance of SimpleXMLElement', \get_class($this), __METHOD__));
    }
    // Find the form field element from the definition.
    $element = $this->findField($name, $group);
    // If the element exists and the attribute exists for the field return the attribute value.
    if ($element instanceof \SimpleXMLElement && \strlen((string) $element[$attribute])) {
        return (string) $element[$attribute];
    } else {
        return $default;
    }
}