def annotate_row(context, row, number, line, data):
    """Return the XHTML markup for the table cell that contains the
        annotation data.

        `context` is the context corresponding to the content being annotated,
        `row` is the tr Element being built, `number` is the line number being
        processed and `line` is the line's actual content.
        `data` is whatever additional data the `get_annotation_data` method
        decided to provide.
        """
