Notations and the Web
<!DOCTYPE image [ <!NOTATION jpeg SYSTEM "http://www.example.org/jpeg"> <!NOTATION png SYSTEM "http://www.example.org/png"> <!ENTITY mypic SYSTEM "foo.jpg" NDATA jpeg> <!ELEMENT image (#PCDATA)*> <!ATTLIST image src ENTITY (jpeg|png) #REQUIRED > ]> <image src="mypic">my picture</image>