.foo {
  position: absolute;
  @debug 10px + 20px;
  display: inline-block;
  @error "Sorry, but `#{$variable}` is not a valid value for $variable.";
}
@debug 10px + 20px;
$wrn: 20px;
@warn "The `border-radius()` mixin will be deprecated in version 2.0.";

.bar {
  position: absolute;
  $wrn: 20px;
  @warn "#{$wrn}";
  display: inline-block;
}

/* http://www.sitepoint.com/using-sasss-error-warn-and-debug-directives/ */
@if unit($input) == 'px' {
  @warn "Please remember to use rem values in the `do-math()` function.";

  // do px math and @return a value;
}