def _make_prefix(self):
        """Create unique anchor prefixes"""

        # Generate a unique anchor prefix so multiple tables
        # can exist on the same HTML page without conflicts.
        fromprefix = "from%d_" % HtmlDiff._default_prefix
        toprefix = "to%d_" % HtmlDiff._default_prefix
        HtmlDiff._default_prefix += 1
        # store prefixes so line format method has access
        self._prefix = [fromprefix,toprefix]
Create unique anchor prefixes