Other meta-information
- <!-- comment -->
- a comment, will be ignored by all processors
- <?target data...?>
- an instruction for a processor, target identifies the processor for
which it is directed, data is a string containing the instruction
- <!ENTITY name value>
- declares an entity with a name and a value, expanded using entity reference:
&name;
(external entities and parameter-entity references are ignored here...)
- <!ELEMENT ...>, <!ATTLIST ...>, ...
- DTD information (briefly mentioned later... - better alternatives: DSD, XML Schema)