Sass 3.2+, media queries, and @content

content.scss

// We had a use-case where we wanted to apply some styles at a certain
// breakpoint *and* to any IEs less than 9 (using the standard .lt-ie9
// class).
//
// The developer tasked with this decided Sass couldn't do it,
// wrote a snarky comment, and then copied and pasted the code twice,
// sort of like this:

@media only screen and (max-width: 500px) {
  a { ... }
  b { ... }
  c { ... }
}

.lt-ie9 {
  a { ... }
  b { ... }
  c { ... } 
}

// You don't need to do that. You can instead use @content like this:

@mixin my-content-mixin {
  @media only screen and (max-width: 500px) {
    @content;
  }
  
  .lt-ie9 {
    @content;
  }
}

@include my-content-mixin {
  a { ... }
  b { ... }
  c { ... }
}

// The output is identical in both cases.