Don't include other component

You must NOT include other Components in a Component. And, You must NOT use ONLY child components, without parent component.

REASON

When you make styles in one Component, you can avoid unintentional layout with Components combination.

Example(1)

BAD

You must NOT include .c-bar into .c-foo, even if you want to change the layout of .c-bar inside of .c-foo.

<div class="c-foo">
    <div class="c-bar"></div>
</div>

scss/object/component/_foo.scss

.c-foo {
    // something style
    .c-bar {
        // something style
    }
}

GOOD

You can resolved above issue by preparing a child component of .c-foo and assign it together with .c-bar.

<div class="c-foo">
    <div class="c-foo__child c-bar"></div>
</div>

scss/object/component/_foo.scss

.c-foo {
    // something style
    &__child {
        // something style
    }
}

Example(2)

BAD

You must NOT use .c-bar__child except for parent component .c-bar.

<div class="c-foo">
    <div class="c-bar__child"></div>
</div>

GOOD

You should wrap child component .c-bar__child by parent component .c-bar.

<div class="c-foo">
    <div class="c-bar">
        <div class="c-bar__child"></div>
    </div>
</div>

Or

<div class="c-foo c-bar">
    <div class="c-bar__child"></div>
</div>