Combining Vendor-Specific CSS Rules: Understanding the Limitations

CSS provides a powerful mechanism for styling elements across different browsers. However, using vendor-specific prefixes in CSS presents a challenge when attempting to consolidate rules that target the same properties.

In particular, combining vendor-specific pseudo-elements/classes into a single rule set raises the question of why this is not possible. To understand this limitation, we delve into the underlying principles of CSS syntax.

According to CSS2.1 specifications, a CSS selector includes everything up to the opening curly brace ({). User agents ignore selectors they cannot parse (i.e., those that do not conform to CSS2.1 standards).

Since browsers may not support vendor-specific prefixes consistently, pseudo-elements/classes with unrecognized prefixes are dropped, leaving only those that are recognized by a specific browser. This explains the inability to combine vendor-specific rules in a comma-separated selector.

The CSS2.1 specification essentially states that ignorance of unknown selectors leads to their rejection, rendering combinations like the one proposed impossible.

This limitation highlights the importance of prefixing vendor-specific rules and recognizing that ultimately, the compatibility of CSS code relies on the browsers' support for specific vendors.