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Naming convention

The name of a BEM entity is unique. The same BEM entity always has the same name in all technologies (CSS, JavaScript, and HTML). The primary purpose of the naming convention is to give names meaning so that they are as informative as possible for the developer.

Compare the same name for a CSS selector that is written in different ways:

To understand the meaning of the first name, you need read through each word carefully. In the last two examples, the name is clearly divided into its parts. But none of these names helps us understand that menu is a block, item is an element, and visible is a modifier. The rules for naming BEM entities were developed in order to make entity names unambiguous and easy to understand.

Naming rules

block-name__elem-name_mod-name_mod-val

Important: Elements of elements do not exist in the BEM methodology. The naming rules do not allow creating elements of elements, but you can nest elements inside each other in the DOM tree.

Examples

In HTML, BEM entities are represented by the class attribute. In BEM, for any of the technologies, there is a call to the class:

Examples of the naming rules are applied to CSS.

Block name

menu

Why don't block names need prefixes?

HTML

<div class="menu">...</div>

CSS

.menu { color: red; }

Element name

menu__item

Important: Identical elements in the same block have the same names. For example, all menu items in the menu block are called menu__item.

HTML

<div class="menu">
    ...
    <span class="menu__item"></span>
</div>

CSS

.menu__item { color: red; }

Block modifier name

menu_hidden

menu_theme_islands

HTML

<div class="menu menu_hidden"> ... </div>
<div class="menu menu_theme_islands"> ... </div>

CSS

.menu_hidden { display: none; }
.menu_theme_islands { color: green; }

Element modifier name

menu__item_visible

menu__item_type_radio

HTML

<div class="menu">
    ...
    <span class="menu__item menu__item_visible menu__item_type_radio"> ... </span>
</div>

CSS

.menu__item_visible {}
.menu__item_type_radio { color: blue; }

Alternative naming schemes

The naming rules above describe the classic approach to naming BEM entities. All BEM tools follow the classic naming scheme by default.

There are alternative solutions that are actively used in the BEM community. To have all technologies apply identical names that were created using alternative naming schemes, use the bem-naming tool. By default, bem-naming is configured to use the methodology's standard naming convention, but it allows you to add rules so you can use alternative schemes.

Two Dashes style

block-name__elem-name--mod-name--mod-val

Important: A double hyphen inside a comment (--) may cause an error during validation of an HTML document.

CamelCase style

blockName-elemName_modName_modVal

React style

BlockName-ElemName_modName_modVal

No Namespace style

_available

This naming scheme limits the use of mixes, because it makes it impossible to determine which block or element a modifier belongs to.

Your naming system

You can create your own custom naming solution for BEM entities. The most important thing is that your new naming system makes it possible to programmatically separate blocks from elements and modifiers.