BEM. Is it possible to mix like this?

Question

css

<section class="buy">
                <div class="buy__input-wrapper">
                    <div class="buy__www buy__help">
                    </div>
                    <div class="buy__select buy__help">
                    </div>
                </div>
</section>

Answer 1

Who will forbid you?
Look at the code of Yandex services, you will see clearly from mixes like
class="link image image_name_googleplay footer-market__promo-image i-bem link_js_inited
" just edit your code after a while.
I use BEM with my variations.