Let's assume that you directly want to render XML contents in a browser. This content may be text-centric XML that you created yourself, contents using a document standard, contents that are pulled out of a database or that are obtained through a web service, e.g. a simple RSS news feed. In most cases, you would use XSLT for styling, i.e. translate XML to HTML or another markup language. However, using CSS is easier and can do a perfect job for some text-centric contents.
CSS for XML is in no way different from CSS for HTML, but you need a browser that implements most of CSS 2 (all modern browsers do).
The only practical difference is that HTML includes default style for each element, e.g. a "h1" title would show in a big font and add space above and below. An XML element like "h1" or "header1" would not show at all. XML elements don't have any default styling. In other words, you will have to define properties for each of your elements. Since CSS implements cascading, you may define defaults for the root elements, or else use the "*" selector.
CSS sometimes is used to make XML editing easier. I.e. the Schema author would produce a CSS that is then used to create a sort of WYSYWIG editing interface. With respect to this functionality, XSLT cannot replace CSS as a rendering solution.
CSS stylesheets are associated with the following processing instruction. Please note that this is different from HTML and XHTML !
<?xml-stylesheet type="text/css" href="some_name.css"?>
Example:
<?xml version="1.0" encoding="ISO-8859-1"?>
<?xml-stylesheet href="stepbystep.css" type="text/css"?>
<!DOCTYPE Stepbystep SYSTEM "stepbystep-ex.dtd">
<Stepbystep xmlns:xlink="http://www.w3.org/1999/xlink">
<Doctitle>Instructions </Doctitle>
.....
</Stepbystep>
When defining style rules for XML elements, you should do the following.
display
attribute.Here is a little example:
/* 1) ---- Definitions that apply to the whole hierarchy */
page { font-family:Times; line-height:1.5;}
page { margin-top:3cm; margin-left:3cm; margin-right:3cm; }
/* 2) ---- title and para are "block" elements with a small margin */
title, para {display: block; margin: 0.5em;}
/* Titles are a bit taller than default size */
title {font-size: 1.5em;}
/* Item are list-item of type bullet */
item {display: list-item;list-style-type: bullet;}
/* strong is an inline element, we render these in italic and blue */
strong {display: inline; font-style: italic; color: rgb(000,000,128);}
A corresponding XML document for this example can be found towards the end of this page.
Below, we explain the use of CSS for XML mostly by example. All example XML and CSS files can be found in the "http://tecfa.unige.ch/guides/xml/examples/css/" directory.
Firstly, let's recall how CSS works. A CSS style sheet is a set of rules (also called rule sets) that describe how to render XML or HTML elements. Each rule has two parts:
The syntax can be summarized as follows:
selector { property:value; property:value; .... }
CSS 2 selectors are introduced in the CSS tutorial. If you are not familiar with CSS properties, read that tutorial (or equivalent) and come back once you understand the basics.
Below we will recall CSS2 selectors, except that example tags are random XML elements and not HTML tags. A selector identifies the element(s) that we will style with properties. CSS 2 selectors work in the same way for HTML, XHTML, HTML5 and any text-centric XML.
Selection of an element (mostly you will use this):
Example:
Step { display: list-item; list-style-type: decimal; }
selection of a child element:
Example:
Step > Title { .... }
selection of descendant element (child, great-child, etc.):
Example:
Step Title { .... }
Combinations:
Example:
DIV OL>LI P
selection of siblings (elements next to each other sharing the same parent):
example:
chapter + section { margin-top: -5mm }
selection of an element that has a certain attribute:
Example:
Title[status] { color: blue; }
(all titles that have a status attribute are rendered in blue )
selection of an element that has an attribute with a given value:
Example:
Title[status="draft"] { color: red; }
Selection of an element that has an attribute with a given value in a comma-separated list:
Title[status~="draft"] { color: blue; }
Rule ordering
Inheritance of properties from parents
Inheritance of properties example: XML
<section>
<title>Here is a title</title>
<para>Here is a paragraph>
</section>
CSS
section {font-family:Arial}
title {font-family:Helvetica}
/* para will inherit font-family from section, i.e. Arial */
XML file: simple-page.xml
<?xml version="1.0" ?>
<?xml-stylesheet href="simple-page.css" type="text/css"?>
<page updated="jan 2007">
<title>Hello friend</title>
<content> Here is some content </content>
<content> Here is some more content :) </content>
<comment> Written by DKS/Tecfa </comment>
</page>
CSS: simple-page.css
/* Definitions that apply to the whole hierarchy */
page { font-family:Times; line-height:1.5;}
/* Margins for the box of the root element */
page { margin-top:3cm; margin-left:3cm; margin-right:3cm; }
/* Block elements */
title, content, comment { display:block; }
title { font-family: Arial; font-size:1.5em;}
content { }
comment { font-style:italic; }
<?xml version="1.0" ?>
<?xml-stylesheet href="simple-list.css" type="text/css"?>
<page updated="jan 2007">
<title>Hello friend</title>
<list>
<item> Here is an item that will be somewhat longer. Here is an item that will be somewhat longer. </item>
<item> Here is item B</item>
<item> Here is a C item </item>
</list>
<comment> Written by DKS/Tecfa , jan 2007 </comment>
</page>
/* Definitions that apply to the whole hierarchy */
page { font-family:Times; line-height:1.5;}
page { margin-top:3cm; margin-left:3cm; margin-right:3cm; }
title, list, comment { display:block; }
title { font-family: Arial; font-size:1.5em;}
item {display:list-item; list-style-position:outside;
list-style-type: disc; }
comment { font-style:italic; }
By default elements of an XML (or HTML) file are displayed in sequential order. It is possible to put an element wherever you wish. Positioning is not easy (avoid if you are new to CSS)
<?xml version="1.0" ?>
<?xml-stylesheet href="simple-positioning.css" type="text/css"?>
<page updated="jan 2007">
<title>Hello friend</title>
<hotstuff>
<item> Here is an item that will be somewhat longer. Here is an item that will be somewhat longer. </item>
<item> Here is item B</item>
<item> Here is a C item </item>
</hotstuff>
<content>
<para> Here is some standard content. Here is some standard content. Here is some standard content. Here is some standard content. Here is some standard content. Here is some standard content. Here is some standard content. Here is some standard content. </para>
<comment> Written by DKS/Tecfa , jan 2007 </comment>
</content>
</page>
/* Definitions that apply to the whole hierarchy */
page { font-family:Times; line-height:1.5;}
/* Margins for the box of the root element */
page { margin-top:3cm; margin-left:3cm; margin-right:3cm; }
/* Block elements */
title, hotstuff, content, comment { display:block; }
title { font-family: Arial; font-size:1.5em;}
content { position: absolute; left: 0; width: 60% }
hotstuff { position: absolute;
right: 0;
width: 20%;
font: 10px/14px verdana, sans-serif;
color: white;
margin: 5px 5px 5px 5px;
padding: 1cm;
background-color: black; }
item {display:list-item; list-style-position:outside; list-style-type: disc; }
comment { font-style:italic; }
CSS isn’t made for data-centric XML, however one can use CSS to add some extra information.
Allows to deal somewhat with data-centric XML. Below is an example.
XML: simple-content.xml
<?xml version="1.0" ?>
<?xml-stylesheet href="simple-content.css" type="text/css"?>
<page updated="jan 2007">
<title>Hello friend</title>
<list>
<item price="10"> White plate </item>
<item price="20"> Gold plate </item>
<item price="15"> Silver plate </item>
</list>
<comment> Written by DKS/Tecfa , jan 2007 </comment>
</page>
CSS: simple-content.css
/* Definitions that apply to the whole heirarchy */
page { font-family:Times; font-size:14pt; line-height:1.5;}
/* Margins for the box of the root element */
page { margin-top:2cm; margin-left:2cm; margin-right:2cm; }
/* Block elements */
title, list, comment { display:block; }
title { font-family: Arial; font-size:1.5em;}
list:before { content:"Products on sale:"; font-size:1.2em; }
item { display:block; }
item:after { content:" - Price: " attr(price) " CHF";}
comment { font-style:italic; }
The :before and :after selectors can be used to add contents before or after element contents (doesn’t work with IE6/7/8)
The content property:
You may add XHTML tags to your XML, but you will have to adjust your DTD or other Schema file in order to keep documents valid. If you only plan to use links but no pictures, you should use XLink. In any case, you also should learn XSLT, a powerful transformation language that allows transforming any XML content into a rendering format like HTML or PDF.
To make your life a bit simpler, you may include XHTML tags in your XML in order to create links and insert pictures. If you use a DTD or another Schema, you should modify these accordingly. Pictures inserted into XML also can be used to style contents. I discourage this, since that way data isn’t anymore separated from styling. Rather learn XSLT !
Below is a simple well-formed XML document that uses a bit of XHTML. Notice how the html namespace xmlns:html="http://www.w3.org/1999/xhtml"
is declared in the root element page
XML: simple-content-htmlns.xml
<?xml version="1.0" ?>
<?xml-stylesheet href="simple-content-htmlns.css" type="text/css"?>
<page xmlns:html="http://www.w3.org/1999/xhtml" updated="jan 2007">
<title>Hello friend</title>
<list>
<html:img src="photo.jpg"/>
<item price="10"> White plate </item>
<item price="20"> Gold plate </item>
<item price="15"> Silver plate </item>
</list>
<comment> Written by DKS/Tecfa , jan 2007 </comment>
</page>
CSS: simple-content-htmlns.css
If you you plan to use XHTML tags, you will have to adjust your DTDs or other schema definitions (if you do use one). Remember: XML knows nothing about anything. The code fragment below shows (1) how to declare the XHTML namespace, and (2) simple versions of the a and img Xhtml elements.
<!ATTLIST YOUR_ROOT_ELEMENT xmlns:html CDATA #FIXED "http://www.w3.org/1999/xhtml">
.....
<!ELEMENT html:img EMPTY>
<!ATTLIST html:img src CDATA #REQUIRED>
<!ELEMENT html:a (#PCDATA)>
<!ATTLIST html:a href CDATA #REQUIRED >
XML with XHTML example
The next example uses XHTML for linking and is available as story-grammar-con-xhtml.dtd, story-grammar-con-xhtml.xml and story-grammar.css
<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT STORY (title, context, problem, goal, THREADS, moral, INFOS)>
<!ATTLIST STORY xmlns:html CDATA #FIXED "http://www.w3.org/1999/xhtml">
<!ELEMENT THREADS (EPISODE+)>
<!ELEMENT EPISODE (subgoal, ATTEMPT+, result) >
<!ELEMENT ATTEMPT (action | EPISODE) >
<!ELEMENT INFOS ( ( date | author | html:a )* ) >
<!ELEMENT title (#PCDATA) >
<!ELEMENT context (#PCDATA|html:img)* >
<!ELEMENT problem (#PCDATA) >
<!ELEMENT goal (#PCDATA) >
<!ELEMENT subgoal (#PCDATA) >
<!ELEMENT result (#PCDATA) >
<!ELEMENT moral (#PCDATA) >
<!ELEMENT action (#PCDATA) >
<!ELEMENT date (#PCDATA) >
<!ELEMENT author (#PCDATA) >
<!ELEMENT html:a (#PCDATA)>
<!ATTLIST html:a
href CDATA #REQUIRED >
<!ELEMENT html:img (#PCDATA)>
<!ATTLIST html:img
src CDATA #REQUIRED >
For a reason I don't understand, the namespace prefix must be called html (e.g. not xh), else IE 8 will not display the link. Firefox would ...
Below is a DTD example using XLink (the XML linking language), available as story-grammar.dtd and story-grammar.xml
<?xml version="1.0"?>
<!ELEMENT STORY (title, context, problem, goal, THREADS, moral, INFOS)>
<!ATTLIST STORY xmlns:xlink CDATA #FIXED "http://www.w3.org/1999/xlink">
<!ELEMENT THREADS (EPISODE+)>
<!ELEMENT EPISODE (subgoal, ATTEMPT+, result) >
<!ELEMENT ATTEMPT (action | EPISODE) >
<!ELEMENT INFOS ( ( date | author | a )* ) >
<!ELEMENT title (#PCDATA) >
<!ELEMENT context (#PCDATA) >
<!ELEMENT problem (#PCDATA) >
<!ELEMENT goal (#PCDATA) >
<!ELEMENT subgoal (#PCDATA) >
<!ELEMENT result (#PCDATA) >
<!ELEMENT moral (#PCDATA) >
<!ELEMENT action (#PCDATA) >
<!ELEMENT date (#PCDATA) >
<!ELEMENT author (#PCDATA) >
<!ELEMENT a (#PCDATA)>
<!ATTLIST a
xlink:href CDATA #REQUIRED
xlink:type CDATA #FIXED "simple"
>
First operations when writing a CSS for XML:
Some example CSS rules
/* title and para elements are blocks. They have an extra margin */
'''title, para {display: block; margin: 0.5em;}'''
/* title element font is 1.5 as big */
'''title {font-size: 1.5em;}'''
/* item elements are list elements, we use bullet style */
'''item {display: list-item;list-style-type: disc;}'''
/* strong is an inline element. Uses italic style and blue color */
'''strong {display: inline; font-style: italic; color: rgb(000,000,128);}'''
See also: CSS tutorial