I am reading it:

Opens the map info window over the icon of the marker. The content of
the info window is given as a DOM node. Only option
GInfoWindowOptions.maxWidth is applicable.

Opens the map info window over the icon of the marker. The content of
the info window is given as a string that contains HTML text. Only
option GInfoWindowOptions.maxWidth is applicable.

Ye, I know the deferent between DOM node and HTML text. but this is an
encapsulation in maps API. As a user, is there another different
between them ?

In recent versions, openInfoWindowHtml and openInfoWindow are
implemented by exactly the same piece of code.

The code now checks the content parameter and if it has "typeof string"
it creates a new <div> node to contain that string and uses that new
node. If the content doesn't have "typeof string" then it assumes that
it is a node.

The processing of the other parameters is identical.

The same also applies for openInfoWindowTabs and openInfoWindowTabsHtml.

--
The Blackpool Community Church Javascript Team
http://www.econym.demon.co.uk/googlemaps/

Ye, I knew the diferent, And, there is no different in recent versions,
but maybe in furture version.
It is that means that I can exchange openInfoWindowHtml with
openInfoWindow in furture version, but suggested correct using for
furture, isn't it?