search
HomeWeb Front-endCSS TutorialWhich Direction Do Selector Engines Read, Exactly?

Which Direction Do Selector Engines Read, Exactly?

"In which direction do selector engines read, exactly?"

The conventional wisdom holds that CSS selector engines commonly read from right to left. However, the precise direction of evaluation can vary depending on the browser and implementation.

Typically, browsers evaluate selectors from right to left to navigate combinators. For instance, in the selector section > div.second > div.third, the engine checks if an element is div.third before examining if its parent is div.second and further up the hierarchy.

Regarding the performance comparison between .name and div.name, the exact order of evaluation can fluctuate and vary broadly across browsers. Even theoretical performance largely relies on the implementation.

Despite the right-to-left evaluation across combinators, it's unlikely that this order extends down to simple selector levels within a compound selector. For example, in the selector div:hover[data-foo="bar"].name:nth-child(5)::after, there's no set guarantee that the criteria will be checked in a strict right-to-left manner.

Instead, certain types of simple selectors may be prioritized for performance reasons. For instance, ID selectors are generally handled first. So, whether a selector is written as div#foo.bar:first-child or div.bar:first-child#foo, Gecko (used by Firefox) will evaluate the ID and class first, regardless of their position.

Ultimately, it's difficult to predict which selector will perform faster in a given context. Performance can differ based on document structure, implementation, and even across different browsers.

The above is the detailed content of Which Direction Do Selector Engines Read, Exactly?. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
A Little Reminder That Pseudo Elements are Children, Kinda.A Little Reminder That Pseudo Elements are Children, Kinda.Apr 19, 2025 am 11:39 AM

Here's a container with some child elements:

Menus with 'Dynamic Hit Areas'Menus with 'Dynamic Hit Areas'Apr 19, 2025 am 11:37 AM

Flyout menus! The second you need to implement a menu that uses a hover event to display more menu items, you're in tricky territory. For one, they should

Improving Video Accessibility with WebVTTImproving Video Accessibility with WebVTTApr 19, 2025 am 11:27 AM

"The power of the Web is in its universality. Access by everyone regardless of disability is an essential aspect."- Tim Berners-Lee

Weekly Platform News: CSS ::marker pseudo-element, pre-rendering web components, adding Webmention to your siteWeekly Platform News: CSS ::marker pseudo-element, pre-rendering web components, adding Webmention to your siteApr 19, 2025 am 11:25 AM

In this week's roundup: datepickers are giving keyboard users headaches, a new web component compiler that helps fight FOUC, we finally get our hands on styling list item markers, and four steps to getting webmentions on your site.

Making width and flexible items play nice togetherMaking width and flexible items play nice togetherApr 19, 2025 am 11:23 AM

The short answer: flex-shrink and flex-basis are probably what you’re lookin’ for.

Position Sticky and Table HeadersPosition Sticky and Table HeadersApr 19, 2025 am 11:21 AM

You can't position: sticky; a

Weekly Platform News: HTML Inspection in Search Console, Global Scope of Scripts, Babel env Adds defaults QueryWeekly Platform News: HTML Inspection in Search Console, Global Scope of Scripts, Babel env Adds defaults QueryApr 19, 2025 am 11:18 AM

In this week's look around the world of web platform news, Google Search Console makes it easier to view crawled markup, we learn that custom properties

IndieWeb and WebmentionsIndieWeb and WebmentionsApr 19, 2025 am 11:16 AM

The IndieWeb is a thing! They've got a conference coming up and everything. The New Yorker is even writing about it:

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Tools

SecLists

SecLists

SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.

EditPlus Chinese cracked version

EditPlus Chinese cracked version

Small size, syntax highlighting, does not support code prompt function

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

SublimeText3 English version

SublimeText3 English version

Recommended: Win version, supports code prompts!

PhpStorm Mac version

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool