A browsing context name is a non-empty string which does not begin with
_ (an underscore), and may be specified as the value of name attributes for
frame elements. Browsing context keywords, i.e. one of
_self (the default),
_top, indicate browsing contexts relative to the current document. Scripts and values of target attributes for
form elements may indicate browsing contexts by either names or keywords.
_selfcontains an element or script.
_parentcontains the element (such as
frame) in which
_selfis embedded, or
_selfif it is not embedded.
_topis not embedded within any other and contains, directly or indirectly, an element or script. This may be equal to either
_parent, or an ancestor of both.
_blankdoes not yet exist, but will be created if a script or element operated by the user sends a URL to it. (A name which is not yet assigned to a browsing context has a similar effect, except the resulting context has a name by which it may be referred to later.)