<===> input.scss
$titles: "foo", "bar", "BaZ";

%border {
        border: 1px solid;
}

@mixin border-red {
        border-color: red;
}

@mixin border-blue {
        border-color: blue;
}

@each $t in $titles {
        p[title="#{$t}" i] {
                @extend %border;
                @include border-red;
        }
        p[title="#{$t}"] {
                @extend %border;
                @include border-blue;
        }
}

<===> output.css
p[title=BaZ], p[title=BaZ i], p[title=bar], p[title=bar i], p[title=foo], p[title=foo i] {
  border: 1px solid;
}

p[title=foo i] {
  border-color: red;
}

p[title=foo] {
  border-color: blue;
}

p[title=bar i] {
  border-color: red;
}

p[title=bar] {
  border-color: blue;
}

p[title=BaZ i] {
  border-color: red;
}

p[title=BaZ] {
  border-color: blue;
}

<===> output-libsass.css
p[title="BaZ"], p[title="BaZ" i], p[title="bar"], p[title="bar" i], p[title="foo"], p[title="foo" i] {
  border: 1px solid;
}

p[title="foo" i] {
  border-color: red;
}

p[title="foo"] {
  border-color: blue;
}

p[title="bar" i] {
  border-color: red;
}

p[title="bar"] {
  border-color: blue;
}

p[title="BaZ" i] {
  border-color: red;
}

p[title="BaZ"] {
  border-color: blue;
}