What is an emphasis marker?

Definition
	An emphasis marker is a word or affix that expresses a speaker's stress upon the predicate of a sentence.

Example (Vietnamese)
	In the following sentence, co is an emphasis marker (diacritical markings have not been included here): on ba co xem quyen truyen ay Mr. Ba EMPHASIS read book story that ‘Mr. Ba did read that novel.’

Generic
	An emphasis marker is a kind of
	What is a word?