Disallow features that are unsupported by the browsers that you are targeting.
.foo { opacity: 1; }
/** ↑
* Features like this, which is unsupported in IE 8 */This rule uses doiuse to detect browser support. doiuse itself checks your code against the "Can I use" database.
doiuse only checks if a browser fully supports a feature. As such, partially supported features will be flagged by this rule.
This is a good rule to use with "warning"-level severity, because its primary purpose is to warn you that you are using features not all browsers fully support and therefore ought to provide fallbacks. But the warning will continue even if you have a fallback in place (it doesn't know); so you probably do not want this rule to break your build. Instead, consider it a friendly reminder to double-check certain spots for fallbacks.
Bugs and feature requests should be reported on the doiuse issue tracker.
Defaults to the doiuse default, which is "> 1%, last 2 versions, Firefox ESR, Opera 12.1".
The following patterns are considered warnings:
.foo { opacity: 0.5; }As IE8 (which as of this writing had just over 1% global usage) does not support opacity:
These options are passed directly to doiuse.
A string interpreted by browserslist that designates precisely which browsers you wish to support. Something like "> 1%, last 2 versions, ie >= 8". For details about the syntax (which is the same as when using Autoprefixer, by the way), please read the browserslist documentation.
If you set browsers: "last 2 versions, ie >=9" the declaration above is allowed.
If you no longer want to be warned about, say, your use of rem, you can use ignore: ["rem"].