v4.0.0

This version makes all usages of tag selectors invalid. This is because accepting child tag selectors allows stylesheets like this, which are against the architecture:

.my-component {}

.my-component > div {}
.my-component > a {}
.my-component > h1 {}
.my-component > div > strong {}

Although it limits the level of nesting this can still lead to unintentionally overriding styles.