In DocBook, parameter entities are mainly used to facilitate customization of the DTD , but they can also be used to control marked sections of a document. The pitarget should be a name that the processing application will recognize. An abstract identifier for an SGML or XML document, DTD , or external entity. To continue the cooking metaphor, raw data is just a set of ingredients. It's up to the processor to select appropriate elements, arrange them for display, and add required presentational information.
Vendors often have proprietary stylesheet formats as well.
In SGML , a local, system-dependent identifier for a document, DTD , or external entity. In XML , a system identifer is required to be a URI . URI is the umbrella term for URN s, URL s, and all other Uniform Resource Identifiers. URL Uniform Resource Locator, a name and address for an existing object accessible over the Internet. Some elements, such as Chapter , have important semantic significance.