Format: "Alias: block/sub-block(modifier, ...).element(modifier, ...)"
For exemple:
<div bem="HeaderMenu: l-header/m-menu(break)"> <!-- m-menu that break, inside l-header, alias "HeaderMenu" -->
<div bem="HeaderMenu.item"> <!-- "HeaderMenu" item element -->
<span bem="HeaderMenu.icon"></span> <!-- "HeaderMenu" icon element -->
<span bem="HeaderMenu/m-icon"></span> <!-- m-icon inside "HeaderMenu" -->
</div>