Sass placeholder class

sass-placeholder-class.css

.container {
  /** 
   **This is an placeholder class
   **/
  display: block;
  margin-left: auto;
  margin-right: auto;
}

.center, .container {
  /** 
   ** This is not an placeholder class
   **/
  text-align: center;
}

sass-placeholder-class.scss

// ----
// Sass (v3.4.9)
// Compass (v1.0.1)
// ----

%center {
  /** 
   **This is an placeholder class
   **/
  display: block;
  margin-left: auto;
  margin-right: auto;
}

.center {
  /** 
   ** This is not an placeholder class
   **/
  text-align: center;
}

.container { 
@extend %center;
@extend .center;
}