Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.3.2)
// ----

.person {
  width: 100%;
  
  &__element {
    width: 80%;
  }
  
  &--modifier {
    width: 90%;
  }
  
  &--modifier & {
    &__element {
      width: 50%;
    }
  }
  
  // as soon as you put the & inside an element the "parent" becomes
  // the wrong tag
  &--modifier-merged {
    width: 20%;
    
    & {
      &__element {
        width: 22%;
      }      
    }
  }
}

SassMeister-output.css

.person {
  width: 100%;
}

.person__element {
  width: 80%;
}

.person--modifier {
  width: 90%;
}

.person--modifier .person__element {
  width: 50%;
}

.person--modifier-merged {
  width: 20%;
}

.person--modifier-merged__element {
  width: 22%;
}