def format_str(text):
    """
    Format some strings.

    This function replacing invalid chars in xml file.
    ex. RSS does't accept C{&} char so it should be replaced to C{&amp;}

    @param text: Text to formating
    @type text: str
    @return: formated text
    @rtype: str
    """
    return text.replace('&', '&amp;')
