What is the correct name for a nested block?

Question

BEM

How to properly name a nested block?
Let's say we have a code:

<main class="main">
        <div class="wrapper">
            <div class="main-left"></div>
            <div class="main-right">
                <a class="link">ссылка</a>
                <div class="mail">
                    <div class="title">title</div>
                    <div class="content"></div>
                </div>
                <div class="elem2">
                    <div class="title">title</div>
                    <div class="content"></div>
                </div>
                ...
            </div>
        </div>
    </main>

PS by BEM

Answer 1

.main
→.main__sidebar
→.main__content
→→.link
→→.elem
→→→.elem__title
→→→.elem__content