1 Introduction
(This section is non-normative.)
Authors might have particular intentions as to how
user agents are to present the information contained in their XML documents.
This specification provides a non-intrusive mechanism, using a processing
instruction, to provide links to one or more style sheets, i.e. resources
specifying the desired rendering in a designated language. User
agents will use these resources to control presentation of XML.
Consider an XHTML document with style sheet associations using the link element:
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Example with link elements</title>
<link rel="stylesheet" href="common.css"/>
<link rel="stylesheet" href="default.css" title="Default style"/>
<link rel="alternate stylesheet" href="alt.css" title="Alternative style"/>
<link rel="stylesheet" href="single-col.css" media="all and (max-width: 30em)"/>
</head>
<body>
...
</body>
</html>
This document could be written as follows, using xml-stylesheet processing instructions:
<?xml-stylesheet href="common.css"?>
<?xml-stylesheet href="default.css" title="Default style"?>
<?xml-stylesheet alternate="yes" href="alt.css" title="Alternative style"?>
<?xml-stylesheet href="single-col.css" media="all and (max-width: 30em)"?>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Example with xml-stylesheet processing instructions</title>
</head>
<body>
...
</body>
</html>
2
Conformance requirements
All diagrams, examples, and notes in this specification are
non-normative, as are all sections explicitly marked non-normative.
Everything else in this specification is normative.
The key words must, must
not, should, should not and may in the normative parts
of this document are to be interpreted as described in RFC 2119. These words do not appear in all uppercase letters in
this specification. [RFC2119]
The following conformance classes are defined by this specification:
- Documents
A document is considered to be a conforming document if it satisfies all must-level criteria in this specification that apply to documents.
xml-stylesheet
processing instructions and their pseudo-attributes are intended for
use by document authors to provide links to and information about one
or more stylesheets, as described in
4 The xml-stylesheet processing instruction, which are
available to be applied to the containing document.
- xml-stylesheet processors
XML defines an application as a software module which receives
the information content of an XML document from an XML processor.
[Definition: An xml-stylesheet processor is such an
application which processes XML processing instructions in accordance
with this specification.] [XML]
An xml-stylesheet processor is considered to be a conforming xml-stylesheet processor if it satisfies all must-level criteria in this specification that apply to xml-stylesheet processors. xml-stylesheet processors do not have to check or enforce any of the constraints on documents.
- Applications
An xml-stylesheet processor may be part of a larger XML
application, or may function independently. In either case,
[Definition: an application is the consumer of the
pseudo-attribute analysis defined in this specification.]
A detailed specification of how applications exploit the
information contained in xml-stylesheet
processing instructions
is out of scope for this document, as this may reasonably vary
from application to application. Accordingly this
specification places no conformance requirements on
applications.
It is however expected that specifications governing the use of
stylesheet languages will reference this specification in
describing how applications may identify stylesheets for
use. Such specifications are expected to specify
interpretations for the values (or absense of value) of those
pseudo-attributes which they make use of, doing so in a way
that is as consistent as possible with those pseudo-attributes'
descriptions in 4 The xml-stylesheet processing instruction,
insofar as this makes sense for the application and stylesheet language(s) in question.
This specification is defined with reference to the vocabulary for
XML provided by the XML Information
Set. [INFOSET]
The productions in this specification use the same
notation as used in the XML specification. Tokens in the
grammar that are not defined in this specification are defined in
the XML specification. [XML]
4 The xml-stylesheet processing instruction
[Definition: A processing instruction information item is said to be a potential xml-stylesheet processing instruction if it has the [target] property xml-stylesheet and it either is in the [children] property of a document information item and appears before the element information item of the document information item's [children] property, or it appears in the [children] property of a document type declaration information item.]
For potential xml-stylesheet processing instructions that are in the [children] property of a document information item, xml-stylesheet processors must report to the application the parsing result of invoking the rules for parsing pseudo-attributes from a string, using the processing instruction information item's [content] property as the string.
For potential
xml-stylesheet processing instructions that are in the [children] property of a document type declaration information item, xml-stylesheet processors may report to the application the parsing result of invoking the rules for parsing pseudo-attributes from a string, using the processing instruction information item's [content] property as the string. [Definition: If it is not reported to the application, the processing instruction information item is said to be ignored.]
Note:
Since non-validating XML processors are not required to read parameter entities or the external subset, it is possible that processing instructions that appear in parameter entities or the external subset will not be present in the document type declaration information item's [children] property. [XML]
[Definition: A potential xml-stylesheet processing instruction is said to be an xml-stylesheet processing instruction if the parsing result is not an error when invoking the rules for parsing pseudo-attributes from a string, using the processing instruction information item's [content] property as the string.]
Documents must not use processing instruction information items with the [target] property
xml-stylesheet if they are not xml-stylesheet processing instructions.
Documents should not use xml-stylesheet processing instructions that are in the [children] property of a document type declaration information item.
An xml-stylesheet processing instruction will match the following production:
Production for xml-stylesheet processing instruction
Documents may specify the following pseudo-attributes on
xml-stylesheet processing instructions, unless otherwise stated:
-
href
Gives the address of the referenced style sheet. Documents must specify this pseudo-attribute. Documents must set the value to a string that matches the grammar for
<IRI-reference> given in RFC 3987. [RFC3987]
-
type
Gives an advisory media type for the referenced style sheet. If
specified, documents must set the value to a string that matches the
media-type production defined in section 3.7 "Media Types"
of RFC 2616. [RFC2616]
Note:
Syntactic conformance to the
production in RFC 2616 is all that is required by the above. This
specification imposes no requirements with respect to the status of the types
used. Some unregistered (as of the publication of this specification) media
types, such as text/xsl, are well-supported by existing
implementations, whereas some registered media types, such as
application/xslt+xml, are not.
The value is advisory in
that it is intended to be used by an application only when no other source of
media type
information becomes available during retrieval of the stylesheet itself.
-
title
Gives the title of the referenced style sheet in a style sheet
set. No constraints beyond those of the PseudoAttValue production
are placed on the value.
-
media
Gives the media for which the referenced style sheet applies. If
specified, documents must set the value to a string that matches the media_query_list production of the Media Queries specification. [MQ]
-
charset
Gives an advisory character encoding for the referenced style
sheet. If specified, documents must set the value to a valid
character encoding name, which must be the name or alias labeled as "preferred MIME name" in the IANA Character Sets registry, if there is one, or the encoding's name, if none of the aliases are so labeled. [IANACHARSET]
The value is advisory in
that it is intended to be used by an application only when no other source of encoding
information becomes available during retrieval of the stylesheet itself, either explicitly via an HTTP header,
or implicitly via its media type, as in the case of XML documents.
-
alternate
If the value is "yes", it
indicates that the referenced style sheet is an alternative style
sheet, and documents must also specify the title
pseudo-attribute with a non-empty value. If specified, documents must set the value to either "yes" or
"no".
Documents must not specify other pseudo-attributes on
xml-stylesheet processing instructions.
Any links to style sheets that are specified externally to the
document (e.g. Link headers in some versions of HTTP [RFC2068]) are considered to create associations that occur before the associations specified by the xml-stylesheet processing instructions. The application is responsible for taking all associations and determining how, if at all, their order affects its processing.