def cdata_section(content):
    """
    Returns a CDATA section for the given ``content``.
    
    CDATA sections are used to escape blocks of text containing characters which would
    otherwise be recognized as markup. CDATA sections begin with the string
    ``<![CDATA[`` and end with (and may not contain) the string 
    ``]]>``. 
    """
    if content is None:
        content = ''
    return "<![CDATA[%s]]>" % content