Placeholder recursion?

[Andrea Maria Piana]

Hi, 

I would like your help to clarify something.

We are using BEM & scss and I have come accross something like (oversimplified):

%some-class {
   font-size: 14px;
   &--active {
      @include %some-class;
   }
}


.some-other-class {
  @include %some-class;
}

The compiled css would be:

.some-other-class {
   font-size: 14px;
}


.some-other-class--active {
  font-size: 14px;
}

To my untrained eye it looks like recursion and I was surprised it compiled. 

I tried to google but could not find much on the topic.

Is this a common pattern? Am I missing something?

Thank you

Andrea