"Silent" classes in LESS

extend.css

foo,
bar {
  background-color: #e0e0e0;
}
foo {
  color: blue;
}
bar {
  color: green;
}

extend.less

@import (reference) "reference";

foo {
  &:extend(.silent);
  color: blue;
}

bar:extend(.silent) {
    color: green;
}

reference.less

.silent {
    background-color: red;
}