The CssSelector Component
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The CssSelector component converts CSS selectors to XPath expressions.
Installation
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$ composer require symfony/css-selectorAlternatively, you can clone the https://github.com/symfony/css-selector repository.
Note
If you install this component outside of a Symfony application, you must
require the vendor/autoload.php file in your code to enable the class
autoloading mechanism provided by Composer. Read
this article for more details.
Usage
See also
This article explains how to use the CssSelector features as an independent component in any PHP application. Read the Symfony Functional Tests article to learn about how to use it when creating Symfony tests.
Why to Use CSS selectors?
When you're parsing an HTML or an XML document, by far the most powerful method is XPath.
XPath expressions are incredibly flexible, so there is almost always an XPath expression that will find the element you need. Unfortunately, they can also become very complicated, and the learning curve is steep. Even common operations (such as finding an element with a particular class) can require long and unwieldy expressions.
Many developers -- particularly web developers -- are more comfortable
using CSS selectors to find elements. As well as working in stylesheets,
CSS selectors are used in JavaScript with the querySelectorAll() function
and in popular JavaScript libraries such as jQuery, Prototype and MooTools.
CSS selectors are less powerful than XPath, but far easier to write, read and understand. Since they are less powerful, almost all CSS selectors can be converted to an XPath equivalent. This XPath expression can then be used with other functions and classes that use XPath to find elements in a document.
The CssSelector Component
2.8
The CssSelectorConverter class was introduced in Symfony 2.8. Previously,
the CssSelector class was used and toXPath was a static method.
The component's only goal is to convert CSS selectors to their XPath equivalents, using toXPath():
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use Symfony\Component\CssSelector\CssSelectorConverter;
$converter = new CssSelectorConverter();
var_dump($converter->toXPath('div.item > h4 > a'));This gives the following output:
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descendant-or-self::div[@class and contains(concat(' ',normalize-space(@class), ' '), ' item ')]/h4/aYou can use this expression with, for instance, DOMXPath or SimpleXMLElement to find elements in a document.
Tip
The Crawler::filter() method uses the CssSelector component to find elements based on a CSS selector string. See the The DomCrawler Component for more details.
Limitations of the CssSelector Component
Not all CSS selectors can be converted to XPath equivalents.
There are several CSS selectors that only make sense in the context of a web-browser.
- link-state selectors:
:link,:visited,:target - selectors based on user action:
:hover,:focus,:active - UI-state selectors:
:invalid,:indeterminate(however,:enabled,:disabled,:checkedand:uncheckedare available)
Pseudo-elements (:before, :after, :first-line,
:first-letter) are not supported because they select portions of text
rather than elements.
Several pseudo-classes are not yet supported:
*:first-of-type,*:last-of-type,*:nth-of-type,*:nth-last-of-type,*:only-of-type. (These work with an element name (e.g.li:first-of-type) but not with*.