UserField::addField

public function addField(array $fields)
{
	$result = new Result();

	if(!array_key_exists('FIELD_NAME', $fields))
	{
		// have to auto-assign field name
		$name = static::getFreeFieldName();

		if(!$name)
		{
			$result->getErrors()->add('ACTION_FAILED', 'Unable to generate field name');
		}

		$fields['FIELD_NAME'] = $name;
	}

	if($result->isSuccess())
	{
		$id = static::add(array_merge($fields, array('ENTITY_ID' => static::getEntityCode())));

		if(!$id)
		{
			static::getApplicationErrors($result);
		}
		else
		{
			$result->setData($id);
		}
	}

	return $result;
}