SassMeister-input-HTML.html

<div class="block">
  <div class="block__element">Stuff</div>
  <div class="block__element--modifier">Red Stuff</div>
  
  <div class="block__element--modifier block__element--and-another">And Another</div>
</div>

SassMeister-input.scss

// ----
// Sass (v3.3.9)
// Compass (v1.0.0.alpha.20)
// ----

.block {
  &__element {
    background-color: #000;
    color: #fff;
    
    &--modifier {
      color: #f00;
    }
    &--and-another {
      color: #ff0;
    }
    &--modifier&--and-another {
      color: #00f;
    }
  }
}

SassMeister-output.css

Invalid CSS after "    &--modifier": expected "{", was "&--and-another {"

"&--and-another" may only be used at the beginning of a compound selector.

SassMeister-rendered.html

<div class="block">
  <div class="block__element">Stuff</div>
  <div class="block__element--modifier">Red Stuff</div>
  
  <div class="block__element--modifier block__element--and-another">And Another</div>
</div>