Clears all errors, but maintains user input. This is useful when a form has been submitted for a semantic other than "process this data". A common example of this is a dependent drop down list; selecting an option in one drop down list forces a refresh submit of the form, to repopulate the options in a second, dependent drop down list.
In these cases, the user input provided in the request is maintained, but any errors should be cleared out (to prevent unwanted error messages and decorations).
@since 3.0.1