The upper right of the following page has a block labelled "How to Format". What's the formal name for this element in GUI design?
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I would call it an Inline Help Box which can take many forms and shapes. Take a look at UI Patterns: Inline Help Box, where they explain the following:
Use to gently introduce functionality to the new and untrained user.
...which is exactly what "How to format" in your screenshot is meant to do.