The design view contains only two subsections (see image) and they are described as following:
Canvas area: this area is used to draw model objects like tables, views, text boxes and relationships. The dashed blue lines are the page delimiters and they are used as a guide in order to avoid that an object is cut when printing the model.
Toggle buttons: these buttons activate some advance widgets. These tools are the model validation, object finder, layers management, executed operations and model objects. Detailed description of each one can be seen in the next sections. Additionally, between the toggle buttons, we have a set of information about the current state of the canvas which are, from left to right, the mouse pointer position (in canvas' coordinate), the current zoom factor, the current selection and the overall width / height of the current selection.