A system identifier is a document-processing construct introduced in the
HyTime
HyTime (''Hypermedia/Time-based Structuring Language'') is a markup language that is an application of SGML. HyTime defines a set of hypertext-oriented element types that, in effect, supplement SGML and allow SGML document authors to build hyperte ...
markup language as a supplement to
SGML
The Standard Generalized Markup Language (SGML; ISO 8879:1986) is a standard for defining generalized markup languages for documents. ISO 8879 Annex A.1 states that generalized markup is "based on two postulates":
* Declarative: Markup should des ...
. It was subsequently incorporated into the
HTML
The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...
and
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...
markup language
Markup language refers to a text-encoding system consisting of a set of symbols inserted in a text document to control its structure, formatting, or the relationship between its parts. Markup is often used to control the display of the document ...
s.
In HyTime, there are two kinds of system identifier: ''formal system identifier'' (FSI) and ''simple system identifier''.
In HTML and XML, a system identifier is a fragmentless
URI reference. It typically occurs in a
Document Type Declaration #REDIRECT Document type declaration #REDIRECT Document type declaration
{{redirect category shell, {{R move{{R from other capitalisation{{R up ...
{{redirect category shell, {{R move{{R from other capitalisation{{R up ...
. In this context, it is intended to identify a document type which is used exclusively in one application, whereas a
identifies a document type that may span more than one application.
In the following example, the system identifier is the text contained within quotes: