Parses a single line.

def parse_line(self, line):
        """
        Parses a single line.
        """

        # Skip blanks
        if line == '':
            return

        # Skip comments
        if regex_comment.search(line):
            return

        # Special case / header: parse global parameters into metadata
        global_parameters = regex_global.search(line)
        if global_parameters:
            self.parse_global_meta(global_parameters.group('parameters'))
            return

        # Tries to check the validity of the line.
        crtf_line = regex_line.search(line)
        if crtf_line:
            # Tries to parse the line.

            # Finds info about the region.
            region = regex_region.search(crtf_line.group('region'))
            type_ = region.group('type') or 'reg'
            include = region.group('include') or '+'
            region_type = region.group('regiontype').lower()
            if region_type in self.valid_definition:
                helper = CRTFRegionParser(self.global_meta, include, type_, region_type,
                                          *crtf_line.group('region', 'parameters'))
                self.shapes.append(helper.shape)
            else:
                self._raise_error("Not a valid CRTF Region type: '{0}'.".format(region_type))

        else:
            self._raise_error("Not a valid CRTF line: '{0}'.".format(line))
            return