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Attribute Modules for CSS - Specification

Attribute Modules (AM) is a technique for using attributes and their values rather than classes for styling HTML elements.


Like other CSS methodologies, AM makes some suggestions about logical groupings for your styling code. These are Modules, Variations & Traits.


Modules are similar to both Blocks and Elements in BEM, and can initially be considered a direct replacement for HTML classes. Modules are described by HTML attributes.


Similar to the Modifier of BEM, Variations are represented by the value of the attribute, and extend or override the base Module's styles.


A collection of single-purpose values, grouped into a namespace by the attribute. For example, a collection of typographical styles might be grouped into a type trait. This is similar to SuitCSS' utils project.

HTML Syntax

The Prefix

All AM attributes must be prefixed in order to avoid clashing with in-built HTML attributes. For the remainder of this document, the prefix am- will be used, but any short string would be appropriate. If the prefix begins with data-, all AM attributes will be valid HTML attributes. Here is an example of AM markup in HTML:

<tag am-traitName="one two mobile:three">
<tag am-BlockName>
<tag am-BlockName-ChildElement>
<tag am-BlockName="variant">


The syntax for attributes follows a similar concept to Suit & BEM, with lower-camel-case names for Traits and upper-camel-case (or Pascal case) for Modules, joined by a hyphen to represent parent-child relationships.

Note: HTML attribute names are not case sensitive, so capitalisation is purely for readability of the HTML markup.


Values are space-separated, like classes, but have a wider range of permitted characters. This is one area where AM provides you extra flexibility, so feel free to experiment.

CSS Syntax

Attribute-value pairs are always styled using the space-separated attribute selector, ~=. This gives precisely the same behaviour as using classes, but each attribute effectively declares its own namespace, affording greater flexibility & isolation in grouping your styles. Here is an example of AM syntax in CSS.

[am-traitName~="value"] { /* styles */ }
[am-traitName~="two"] { /* styles */ }
[am-traitName~="three"], .breakpoint-mobile [am-traitName~="mobile:three"] { /* styles */ }

[am-BlockName] {
  /* Block Styles */
[am-BlockName~="modifier"] {
  /* Variant Styles */

[am-BlockName-ChildElement] {
  /* Child Block Styles */

Note the use of the base attribute selector for styling - these styles are shared by all tags that include the attribute. This is an ideal behaviour for Modules & Variations, as a Variation cannot exist without a base Module styles to be based on. In contrast, a Trait usually doesn't define any styles at the base attribute, but provides a series of individual styles that can be mixed and matched.


The Attribute-Module CSS (AMCSS) Specification







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