what are the other codes which can be written instead of "_blank"?

Answer 1

_blank|_self|_parent|_top|framename

_blank Opens the linked document in a new window or tab
_self Opens the linked document in the same frame as it was clicked (this is default)
_parent Opens the linked document in the parent frame
_top Opens the linked document in the full body of the window
framename Opens the linked document in a named frame