def to_csv(self,
               filename=None,
               as_text=True,
               use_descriptions=False,
               dlm=",",
               header=True):
        """
        Returns a CSV string built from the summaries of the Intervals.

        Args:
            use_descriptions (bool): Whether to use descriptions instead
                of summaries, if available.
            dlm (str): The delimiter.
            header (bool): Whether to form a header row.

        Returns:
            str: A string of comma-separated values.
        """
        if (filename is None):
            if (not as_text):
                raise StriplogError("You must provide a filename or set as_text to True.")
        else:
            as_text = False

        if as_text:
            output = StringIO()
        else:
            output = open(filename, 'w')

        fieldnames = ['Top', 'Base', 'Component']
        writer = csv.DictWriter(output,
                                delimiter=dlm,
                                fieldnames=fieldnames,
                                quoting=csv.QUOTE_MINIMAL)

        if header:
            writer.writeheader()

        for i in self.__list:
            if use_descriptions and i.description:
                text = i.description
            elif i.primary:
                text = i.primary.summary()
            else:
                text = ''
            data = {j: k for j, k in zip(fieldnames, [i.top.z, i.base.z, text])}
            writer.writerow(data)

        if as_text:
            return output.getvalue()
            #return output
        else:
            output.close
            return None
Returns a CSV string built from the summaries of the Intervals.

        Args:
            use_descriptions (bool): Whether to use descriptions instead
                of summaries, if available.
            dlm (str): The delimiter.
            header (bool): Whether to form a header row.

        Returns:
            str: A string of comma-separated values.