A message bar informing the user of the state of the system/page/function
Use a contextual alert to highlight a piece of information, often a deviation, with a contrasting background.
Contextual help button
A button that will present an explanation to a problem/question.
General form error
Summarising the errors that has occured in a form, or signal an error that doesn't relate to a single field, but rather a combination that is invalid.
Design descriptions to follow.