class for <p> elements containing only <img>s
In the editor, a <p> containing nothing but plugins gets turned into a <div>.
However, it's still shown a little confusingly as a <p> to the user.
Can the editor tell whether a <p> contains nothing but <img>s? If so, it should put a class = "fake-paragraph" (or something) on it. Then the CSS can be amended appropriately so that the user sees a more useful clue.