BEM: the separation of blocks from layout

Question

Let's say I have to define a header block in BEM. Headers need some indentation (padding, margins), but it's also a common understanding that layout should stay separated from components.

The question is, should I specify indentation as a part of my header block CSS, or should it only be provided by surrounding blocks (layout blocks or grid)? Both approaches have their cons and pros.

Answer 1

You can mix few blocks (or block and element of some other block) on the same DOM-node.

E.g. <div class="header layout__header">.