In some cases, authors may want user agents to render content that does not come from the
document tree. One familiar example of this is a numbered list; the author does not want to list the numbers explicitly, he or she wants the user agent to generate them automatically. Similarly, authors may want the user agent to insert the word "Figure" before the caption of a figure, or "Chapter 7" before the seventh chapter title. For audio or braille in particular, user agents should be able to insert these strings.
In CSS 2.1, content may be generated by two mechanisms:
- The 'content' property, in conjunction with the :before and :after pseudo-elements.
- Elements with a value of 'list-item' for the 'display' property.
Authors specify the style and location of generated content with the :before and :after pseudo-elements. As their names indicate, the :before and :after pseudo-elements specify the location of content before and after an element's
document tree content. The
'content' property, in conjunction with these pseudo-elements, specifies what is inserted.
For example, the following rule inserts the string "Note: " before the content of every P element whose "class" attribute has the value "note":
p.note:before { content: "Note: " }
The formatting objects (e.g., boxes) generated by an element include generated content. So, for example, changing the above style sheet to:
p.note:before { content: "Note: " }
p.note { border: solid green }
would cause a solid green border to be rendered around the entire paragraph, including the initial string.
The :before and :after pseudo-elements
inherit any inheritable properties from the element in the document tree to which they are attached.
For example, the following rules insert an open quote mark before every Q element. The color of the quote mark will be red, but the font will be the same as the font of the rest of the Q element:
q:before {
content: open-quote;
color: red
}
In a :before or :after pseudo-element declaration, non-inherited properties take their
initial values.
So, for example, because the initial value of the
'display' property is 'inline', the quote in the previous example is inserted as an inline box (i.e., on the same line as the element's initial text content). The next example explicitly sets the
'display' property to 'block', so that the inserted text becomes a block:
body:after {
content: "The End";
display: block;
margin-top: 2em;
text-align: center;
}
The :before and :after pseudo-elements interact with other boxes as if they were real elements inserted just inside their associated element.
For example, the following document fragment and style sheet:
<p> Text </p> p:before { display: block; content: 'Some'; }
...would render in exactly the same way as the following document fragment and style sheet:
<p><span>Some</span> Text </p> span { display: block }
Similarly, the following document fragment and style sheet:
<h2> Header </h2> h2:after { display: block; content: 'Thing'; }
...would render in exactly the same way as the following document fragment and style sheet:
<h2> Header <span>Thing</span></h2> h2 { display: block; }
span { display: block; }
Note. This specification does not fully define the interaction of :before and :after with replaced elements (such as IMG in HTML). This will be defined in more detail in a future specification.
- 'content'
| Value: | normal | none | [ <string> | <uri> | <counter> | attr(<identifier>) | open-quote | close-quote | no-open-quote | no-close-quote ]+ | inherit |
| Initial: | normal |
| Applies to: | :before and :after pseudo-elements |
| Inherited: | no |
| Percentages: | N/A |
| Media: | all |
| Computed value: | On elements, always computes to 'normal'. On :before and :after, if 'normal' is specified, computes to 'none'. Otherwise, for URI values, the absolute URI; for attr() values, the resulting string; for other keywords, as specified. |
This property is used with the :before and :after pseudo-elements to generate content in a document. Values have the following meanings:
- none
- The pseudo-element is not generated.
- normal
- Computes to 'none' for the :before and :after pseudo-elements.
- <string>
- Text content (see the section on strings).
- <uri>
- The value is a URI that designates an external resource (such as an image). If the user agent cannot display the resource it must either leave it out as if it were not specified or display some indication that the resource cannot be displayed.
- <counter>
- Counters may be specified with two different functions: 'counter()' or 'counters()'. The former has two forms: 'counter(name)' or 'counter(name, style)'. The generated text is the value of the innermost counter of the given name in scope at this pseudo-element; it is formatted in the indicated style ('decimal' by default). The latter function also has two forms: 'counters(name, string)' or 'counters(name,string, style)'. The generated text is the value of all counters with the given name in scope at this pseudo-element, from outermost to innermost separated by the specified string. The counters are rendered in the indicated style ('decimal' by default). See the section onautomatic counters and numbering for more information. The name must not be 'none', 'inherit' or 'initial'. Such a name causes the declaration to be ignored.
- open-quote and close-quote
- These values are replaced by the appropriate string from the 'quotes' property.
- no-open-quote and no-close-quote
- Introduces no content, but increments (decrements) the level of nesting for quotes.
- attr(X)
- This function returns as a string the value of attribute X for the subject of the selector. The string is not parsed by the CSS processor. If the subject of the selector does not have an attribute X, an empty string is returned. The case-sensitivity of attribute names depends on the document language.
Note. In CSS 2.1, it is not possible to refer to attribute values for other elements than the subject of the selector.
The
'display' property controls whether the content is placed in a block or inline box.
The following rule causes the string "Chapter: " to be generated before each H1 element:
H1:before {
content: "Chapter: ";
display: inline;
}
Authors may include newlines in the generated content by writing the "\A" escape sequence in one of the strings after the
'content' property. This inserted line break is still subject to the
'white-space' property. See
"Strings" and
"Characters and case" for more information on the "\A" escape sequence.
h1:before {
display: block;
text-align: center;
white-space: pre;
content: "chapter\A hoofdstuk\A chapitre"
}
Generated content does not alter the document tree. In particular, it is not fed back to the document language processor (e.g., for reparsing).
In CSS 2.1, authors may specify, in a style-sensitive and context-dependent manner, how user agents should render quotation marks. The
'quotes' property specifies pairs of quotation marks for each level of embedded quotation. The
'content' property gives access to those quotation marks and causes them to be inserted before and after a quotation.
- 'quotes'
| Value: | [<string> <string>]+ | none | inherit |
| Initial: | depends on user agent |
| Applies to: | all elements |
| Inherited: | yes |
| Percentages: | N/A |
| Media: | visual |
| Computed value: | as specified |
This property specifies quotation marks for any number of embedded quotations. Values have the following meanings:
- none
- The 'open-quote' and 'close-quote' values of the 'content' property produce no quotation marks.
- [<string> <string>]+
- Values for the 'open-quote' and 'close-quote' values of the 'content' property are taken from this list of pairs of quotation marks (opening and closing). The first (leftmost) pair represents the outermost level of quotation, the second pair the first level of embedding, etc. The user agent must apply the appropriate pair of quotation marks according to the level of embedding.
For example, applying the following style sheet:
/* Specify pairs of quotes for two levels in two languages */
q:lang(en) { quotes: '"' '"' "'" "'" }
q:lang(no) { quotes: "«" "»" '"' '"' }
/* Insert quotes before and after Q element content */
q:before { content: open-quote }
q:after { content: close-quote }
to the following HTML fragment:
<HTML lang="en">
<HEAD>
<TITLE>Quotes</TITLE>
</HEAD>
<BODY>
<P><Q>Quote me!</Q>
</BODY>
</HTML>
would allow a user agent to produce:
"Quote me!"
while this HTML fragment:
<HTML lang="no">
<HEAD>
<TITLE>Quotes</TITLE>
</HEAD>
<BODY>
<P><Q>Trøndere gråter når <Q>Vinsjan på kaia</Q> blir deklamert.</Q>
</BODY>
</HTML>
would produce:
«Trøndere gråter når "Vinsjan på kaia" blir deklamert.»
Note. While the quotation marks specified by 'quotes' in the previous examples are conveniently located on computer keyboards, high quality typesetting would require different ISO 10646 characters. The following informative table lists some of the ISO 10646 quotation mark characters:
| Character | Approximate rendering | ISO 10646 code (hex) | Description |
|---|
| " | " | 0022 | QUOTATION MARK [the ASCII double quotation mark] |
| ' | ' | 0027 | APOSTROPHE [the ASCII single quotation mark] |
| ‹ | < | 2039 | SINGLE LEFT-POINTING ANGLE QUOTATION MARK |
| › | > | 203A | SINGLE RIGHT-POINTING ANGLE QUOTATION MARK |
| « | « | 00AB | LEFT-POINTING DOUBLE ANGLE QUOTATION MARK |
| » | » | 00BB | RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK |
| ‘ | ` | 2018 | LEFT SINGLE QUOTATION MARK [single high-6] |
| ’ | ' | 2019 | RIGHT SINGLE QUOTATION MARK [single high-9] |
| “ | `` | 201C | LEFT DOUBLE QUOTATION MARK [double high-6] |
| ” | '' | 201D | RIGHT DOUBLE QUOTATION MARK [double high-9] |
| „ | ,, | 201E | DOUBLE LOW-9 QUOTATION MARK [double low-9] |
