'Set string value of *name* property to *value*.'

def _set_element_text(self, prop_name, value):

    value = str(value)
    if (len(value) > 255):
        tmpl = u"exceeded    255    char    limit    for    property,    got:\n\n'%s'"
        raise ValueError((tmpl % value))
    element = self._get_or_add(prop_name)
    element.text = value
