This element represents stress emphasis of its contents. The level of emphasis that a particular piece of content has is given by its number of ancestor EM elements. The 'stress' being referred to is linguistic. If spoken, this stress would be emphasised pronunciation on a word that can change the nuance of a sentence.
This element represents an integration point for an external (typically non-HTML) application or interactive content. The optional src attribute specifies the URL of the resource being embedded.