'Iterate through panel items each represented as a tuple of
(panel_key, panel_type, panel_content).'

def panel_items_iter(self):

    for (panel_key, panel_value) in iteritems(self.panel_items()):
        if (panel_value is None):
            continue
        panel_type = panel_item_types.SECTION
        if panel_key.startswith('tool_'):
            panel_type = panel_item_types.TOOL
        elif panel_key.startswith('label_'):
            panel_type = panel_item_types.LABEL
        elif panel_key.startswith('workflow_'):
            panel_type = panel_item_types.WORKFLOW
        (yield (panel_key, panel_type, panel_value))
