NAME¶
CSS::DOM - Document Object Model for Cascading Style Sheets
VERSION¶
Version 0.14
This is an alpha version. The API is still subject to change. Many features have
not been implemented yet (but patches would be welcome :-).
The interface for feeding CSS code to CSS::DOM changed incompatibly in version
0.03.
SYNOPSIS¶
use CSS::DOM;
my $sheet = CSS::DOM::parse( $css_source );
use CSS::DOM::Style;
my $style = CSS::DOM::Style::parse(
'background: red; font-size: large'
);
my $other_sheet = new CSS::DOM; # empty
$other_sheet->insertRule(
'a{ text-decoration: none }',
$other_sheet->cssRules->length,
);
# etc.
# access DOM properties
$other_sheet->cssRules->[0]->selectorText('p'); # change it
$style->fontSize; # returns 'large'
$style->fontSize('small'); # change it
DESCRIPTION¶
This set of modules provides the CSS-specific interfaces described in the W3C
DOM recommendation.
The CSS::DOM class itself implements the StyleSheet and CSSStyleSheet DOM
interfaces.
This set of modules has two modes:
- 1.
- It can validate property values, ignoring those that are
invalid (just like a real web browser), and support shorthand properties.
This means you can set font to '13px/15px My Font' and have the font-size,
line-height, and font-family properties (among others) set automatically.
Also, "color: green; color: kakariki" will assign 'green' to the
color property, 'kakariki' not being a recognised color value.
- 2.
- It can blithely accept all property assignments as being
valid. In the case of "color: green; color kakariki", 'kakariki'
will be assigned, since it overrides the previous assignment.
These two modes are controlled by the "property_parser" option to the
constructors.
CONSTRUCTORS¶
- CSS::DOM::parse( $string )
- This method parses the $string and returns a style sheet
object. If you just have a CSS style declaration, e.g., from an HTML
"style" attribute, see "parse" in
CSS::DOM::Style.
- new CSS::DOM
- Creates a new, empty style sheet object. Use this only if
you plan to build the style sheet piece by piece, instead of parsing a
block of CSS code.
You can pass named arguments to both of those. "parse" accepts all of
them; "new" understands only the first two,
"property_parser" and "url_fetcher".
- property_parser
- Set this to a PropertyParser object to specify which
properties are supported and how they are parsed.
If this option is not specified or is set to "undef", all property
values are treated as valid.
See CSS::DOM::PropertyParser for more details.
- url_fetcher
- This has to be a code ref that returns the contents of the
style sheet at the URL passed as the sole argument. E.g.,
# Disclaimer: This does not work with relative URLs.
use LWP::Simple;
use CSS::DOM;
$css = '@import "file.css"; /* other stuff ... ';
$ss = CSS::DOM::parse $css, url_fetcher => sub { get shift };
$ss->cssRules->[0]->styleSheet; # returns a style sheet object
# corresponding to file.css
The subroutine can choose to return "undef" or an empty list, in
which case the @import rule's "styleSheet" method will return
null (empty list or "undef"), as it would if no
"url_fetcher" were specified.
It can also return named items after the CSS code, like this:
return $css_code, decode => 1, encoding_hint => 'iso-8859-1';
These correspond to the next two items:
- decode
- If this is specified and set to a true value, then CSS::DOM
will treat the CSS code as a string of bytes, and try to decode it based
on @charset rules and byte order marks.
By default it assumes that it is already in Unicode (i.e., decoded).
- encoding_hint
- Use this to provide a hint as to what the encoding might
be.
If this is specified, and "decode" is not, then "decode =>
1" is assumed.
STYLE SHEET ENCODING¶
See the options above. This section explains how and when you
should use
those options.
According to the CSS spec, any encoding specified in the 'charset' field on an
HTTP Content-Type header, or the equivalent in other protocols, takes
precedence. In such a case, since CSS::DOM doesn't deal with HTTP, you have to
decode it yourself.
Otherwise, you should use "decode => 1" to instruct CSS::DOM to use
byte order marks or @charset rules.
If neither of those is present, then encoding data in the referencing document
(e.g., <link charset="..."> or an HTML document's own
encoding), if available/applicable, should be used. In this case, you should
use the "encoding_hint" option, so that CSS::DOM has something to
fall back to.
If you use "decode => 1" with no encoding hint, and no BOM or
@charset is to be found, UTF-8 is assumed.
SYNTAX ERRORS¶
The two constructors above, and also "CSS::DOM::Style::parse", set $@
to the empty string upon success. If they encounter a syntax error, they set
$@ to the error and return an object that represents whatever was parsed up to
that point.
Other methods that parse CSS code might die on encountering syntax errors, and
should usually be wrapped in an "eval".
The parser follows the 'future-compatible' syntax described in the CSS 2.1
specification, and also the spec's rules for handling parsing errors. Anything
not handled by those two is a syntax error.
In other words, a syntax error is one of the following:
- •
- An unexpected closing bracket, as in these examples
a { text-decoration: none )
*[name=~'foo'} {}
#thing { clip: rect( ]
- •
- An HTML comment delimiter within a rule; e.g.,
a { text-decoration : none <!-- /* Oops! */ }
<!-- /*ok*/ @media --> /* bad! */ print { }
- •
- An extra "@" keyword or semicolon where it
doesn't belong; e.g.,
@media @print { .... }
@import "file.css" @print;
td, @page { ... }
#tabbar td; #tab1 { }
OBJECT METHODS¶
Attributes¶
- type
- Returns the string 'text/css'.
- disabled
- Allows one to specify whether the style sheet is used.
(This attribute is not actually used yet by CSS::DOM.) You can set it by
passing an argument.
- ownerNode
- Returns the node that 'owns' this style sheet.
- parentStyleSheet
- If the style sheet belongs to an '@import' rule, this
returns the style sheet containing that rule. Otherwise it returns an
empty list.
- href
- Returns the style sheet's URI, if applicable.
- title
- Returns the value of the owner node's title attribute.
- media
- Returns the MediaList associated with the style sheet (or a
plain list in list context). This defaults to an empty list. You can pass
a comma-delimited string to the MediaList's "mediaText" method
to initialise it.
(The medium information is not actually used [yet] by CSS::DOM, but you can
put it there.)
- ownerRule
- If this style sheet was created by an @import rule, this
returns the rule; otherwise it returns an empty list (or undef in scalar
context).
- cssRules
- In scalar context, this returns a CSS::DOM::RuleList object
(simply a blessed array reference) of CSS::DOM::Rule objects. In list
context it returns a list.
Methods¶
- insertRule ( $css_code, $index )
- Parses the rule contained in the $css_code, inserting it in
the style sheet's list of rules at the given $index.
- deleteRule ( $index )
- Deletes the rule at the given $index.
- hasFeature ( $feature, $version )
- You can call this either as an object or class method.
This is actually supposed to be a method of the 'DOMImplementation' object.
(See, for instance, HTML::DOM::Interface's method of the same name, which
delegates to this one.) This returns a boolean indicating whether a
particular DOM module is implemented. Right now it returns true only for
the 'CSS2' and 'StyleSheets' features (version '2.0').
Non-DOM Methods¶
- set_ownerNode
- This allows you to set the value of "ownerNode".
Passing an argument to "ownerNode" does nothing, because it is
supposed to be read-only. But you have to be able to set it somehow, so
that's why this method is here.
The style sheet will hold a weak reference to the object passed to this
method.
- set_href
- Like "set_ownerNode", but for
"href".
- property_parser
- url_fetcher
- These two both return what was passed to the constructor.
The second one, "url_fetcher" also allows an assignment, but
this is not propagated to sub-rules and is intended mainly for internal
use.
FUNCTIONS¶
- CSS::DOM::parse
- See "CONSTRUCTORS", above.
- CSS::DOM::compute_style( %options )
- Warning: This is still highly experimental and
crawling with bugs.
This computes the style for a given HTML element. It does not yet calculate
actual measurements (e.g., converting percentages to pixels), but simply
applies the cascading rules and selectors. Pseudo-classes are not yet
supported (but pseudo-elements are).
The precedence rules for normal vs important declarations in the CSS 2
specification are used. (CSS 2.1 is unclear.) The precedence is as
follows, from lowest to highest:
user agent normal declarations
user normal declarations
author normal "
user agent !important declarations
author !important "
user " "
The %options are as follows. They are all optional except for
"element".
- ua_sheet
- The user agent style sheet
- user_sheet
- The user style sheet
- author_sheets
- Array ref of style sheets that the HTML document defines or
links to.
- element
- The element
- pseudo
- The pseudo-element (e.g., 'first-line'). This can be
specified with no colons (the way Opera requires it) or with one or two
colons (the way Firefox requires it).
- medium
- height
- width
- ppi
- (To be implemented)
CLASSES AND DOM INTERFACES¶
Here are the inheritance hierarchy of CSS::DOM's various classes and the DOM
interfaces those classes implement. For brevity's sake, a simple '::' at the
beginning of a class name in the left column is used for 'CSS::DOM::'. Items
in brackets do not exist yet. (See also CSS::DOM::Interface for a
machine-readable list of standard methods.)
Class Inheritance Hierarchy Interfaces
--------------------------- ----------
CSS::DOM StyleSheet, CSSStyleSheet
::Array
::MediaList MediaList
::StyleSheetList StyleSheetList
::RuleList CSSRuleList
::Rule CSSRule, CSSUnknownRule
::Rule::Style CSSStyleRule
::Rule::Media CSSMediaRule
::Rule::FontFace CSSFontFaceRule
::Rule::Page CSSPageRule
::Rule::Import CSSImportRule
::Rule::Charset CSSCharsetRule
::Style CSSStyleDeclaration, CSS2Properties
::Value CSSValue
::Value::Primitive CSSPrimitiveValue, RGBColor, Rect
::Value::List CSSValueList
[::Counter Counter]
CSS::DOM does not implement the following interfaces (see HTML::DOM for these):
LinkStyle
DocumentStyle
ViewCSS
DocumentCSS
DOMImplementationCSS
ElementCSSInlineStyle
IMPLEMENTATION NOTES¶
- •
- Attributes of objects are accessed via methods of the same
name. When the method is invoked, the current value is returned. If an
argument is supplied, the attribute is set (unless it is read-only) and
its old value returned.
- •
- Where the DOM spec. says to use null, undef or an empty
list is used.
- •
- Instead of UTF-16 strings, CSS::DOM uses Perl's Unicode
strings.
- •
- Each method that the specification says returns an
array-like object (e.g., a RuleList) will return such an object in scalar
context, or a simple list in list context. You can use the object as an
array ref in addition to calling its "item" and
"length" methods.
PREREQUISITES¶
perl 5.8.2 or higher
Exporter 5.57 or later
Encode 2.10 or higher
Clone 0.09 or higher
BUGS¶
The parser has not been updated to conform to the April 2009 revision of the CSS
2.1 candidate recommendation. Specifically, unexpected closing brackets are
not ignored, but cause syntax errors; and @media rules containing unrecognised
statements are themselves currently treated as unrecognised (the unrecognised
inner statements should be ignored, rendering the outer @media rule itself
valid).
If you create a custom property parser that defines 'list-style-type' to include
multiple tokens, then counters will become "CSS_CUSTOM" CSSValue
objects instead of "CSS_COUNTER" CSSPrimitiveValue objects.
If you change a property parser's property definitions such that a primitive
value becomes a list, or vice versa, and then try to modify the
"cssText" property of an existing value object belonging to that
property, things will go awry.
Whitespace and comments are sometimes preserved in serialised CSS and sometimes
not. Expect inconsistency.
To report bugs, please e-mail the author.
ACKNOWLEDGEMENTS¶
Thanks to Ville SkyttA~X and Nicholas Bamber for their contributions.
AUTHOR & COPYRIGHT¶
Copyright (C) 2007-10 Father Chrysostomos <sprout [at] cpan [dot] org>
This program is free software; you may redistribute it and/or modify it under
the same terms as perl. The full text of the license can be found in the
LICENSE file included with this module.
SEE ALSO¶
All the classes listed above under "CLASSES AND DOM INTERFACES".
CSS::SAC, CSS.pm and HTML::DOM
The DOM Level 2 Style specification at
<
http://www.w3.org/TR/DOM-Level-2-Style>
The CSS 2.1 specification at <
http://www.w3.org/TR/CSS21/>