Multiple Elements with Same ID: A Journey into Invalidity
Despite the clear guidance from W3C that no two elements in a page should share the same ID, a puzzling phenomenon arises when multiple elements possess identical IDs. Let's investigate the implications of this anomaly.
Browser Behavior
Browsers often adopt a "fail silently" approach, interpreting invalid HTML to conform to their expectations. Thus, while it is invalid, the HTML example with two elements having the same ID works in all browsers.
Potential Side Effects
However, by deviating from the specification, you open the door to unforeseen consequences. For instance, using the getElementById() method will only retrieve the first element with the specified ID.
A Safer Alternative
Instead of using multiple elements with the same ID, employ class names for styling groups of elements. This practice adheres to the intended design of CSS selectors.
Querying Elements with the Same ID
If you absolutely must select multiple elements with the same ID, you can resort to attribute selectors:
document.querySelectorAll('p[id="red"]');
Note that this approach may not work in older browser versions such as IE7 and below.
Conclusion
While browsers may accommodate invalid HTML, it is strongly advised against relying on such behavior. For consistency, maintainability, and to avoid potential issues, use class names for styling similar elements.
The above is the detailed content of What Happens When You Use Duplicate IDs in HTML?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undress AI Tool
Undress images for free

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

There are three ways to selectively include CSS on a specific page: 1. Inline CSS, suitable for pages that are not frequently accessed or require unique styles; 2. Load external CSS files using JavaScript conditions, suitable for situations where flexibility is required; 3. Containment on the server side, suitable for scenarios using server-side languages. This approach can optimize website performance and maintainability, but requires balance of modularity and performance.

CSS blocks page rendering because browsers view inline and external CSS as key resources by default, especially with imported stylesheets, header large amounts of inline CSS, and unoptimized media query styles. 1. Extract critical CSS and embed it into HTML; 2. Delay loading non-critical CSS through JavaScript; 3. Use media attributes to optimize loading such as print styles; 4. Compress and merge CSS to reduce requests. It is recommended to use tools to extract key CSS, combine rel="preload" asynchronous loading, and use media delayed loading reasonably to avoid excessive splitting and complex script control.

In the following tutorial, I will show you how to create Lottie animations in Figma. We'll use two colorful designs to exmplify how you can animate in Figma, and then I'll show you how to go from Figma to Lottie animations. All you need is a free Fig

We put it to the test and it turns out Sass can replace JavaScript, at least when it comes to low-level logic and puzzle behavior. With nothing but maps, mixins, functions, and a whole lot of math, we managed to bring our Tangram puzzle to life, no J

ThebestapproachforCSSdependsontheproject'sspecificneeds.Forlargerprojects,externalCSSisbetterduetomaintainabilityandreusability;forsmallerprojectsorsingle-pageapplications,internalCSSmightbemoresuitable.It'scrucialtobalanceprojectsize,performanceneed

No,CSSdoesnothavetobeinlowercase.However,usinglowercaseisrecommendedfor:1)Consistencyandreadability,2)Avoidingerrorsinrelatedtechnologies,3)Potentialperformancebenefits,and4)Improvedcollaborationwithinteams.

CSSCounters is a tool for creating automatic numbers. 1. Basic usage: define and operate counters through counter-reset and counter-increment, such as "SectionX." before h2. 2. Advanced usage: Use nested counters to create complex numbers, such as chapter and section numbers. 3. Notes: Ensure the counter is reset correctly, optimize performance, and simplify counter logic. 4. Best practice: clear naming, define counters in CSS, and use counter-increment and counter-reset reasonably.

CSSismostlycase-insensitive,butURLsandfontfamilynamesarecase-sensitive.1)Propertiesandvalueslikecolor:red;arenotcase-sensitive.2)URLsmustmatchtheserver'scase,e.g.,/images/Logo.png.3)Fontfamilynameslike'OpenSans'mustbeexact.
