[whatwg] External document subset support

[Kristof Zelechovski]

The localization of your site starts with connection negotiation where the
representation of resources served depends on the browser's language of
choice.  Configuring the server to support this needs some technical
expertise, and so does using a server-side scripting language.
External DTD support is not required for entities; they may be repeated in
the internal subset for Safari.  This repetition is only a minor nuisance to
the editor because only the entities that the text actually includes are
needed, which usually amounts to a few entities for symbols (right arrow
family) and typographic marks (non-breaking space family).  (I am talking
about standard entities here, not entities for customization that are likely
to change; such use should be discouraged).  If everything else fails, the
internal subset may be provided as a server-side include.
IMHO,
Chris