Retina.js

Dynamically swaps img src and background URLs based on device pixel density using Apple's @2x/@3x convention, as detailed in the 'How it works' section for both tags and inline styles.

Works with modern browsers and gracefully degrades back to IE6, ensuring broad support without breaking older environments, as highlighted in the 'Compatibility' section.

Provides ready-to-use mixins for SCSS, Sass, Less, and Stylus to generate media queries for background images, simplifying responsive CSS workflows across different preprocessors.

Allows explicit high-res paths via the data-rjs attribute, useful for custom setups like Ruby on Rails with asset digesting, where automatic detection fails.