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.filter:extend(.btn-group all) {}
 button:extend(.btn-default, .btn all) {}
.filter > button:extend(.btn-group > .btn all) {}

// also don't miss that there're a lot of classes like
// .btn-group-xs .btn-xs etc. etc.
// and none of those are considered by above code
// (so you also have to code them explicitly when needed)

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.font-face(@family, @filename: @family) {

    // font-family and font file name don't have to be the same but let's keep it simple

    font-family: "@{family}";
    
    @font-face {
        font-family: "@{family}";
        @file: "../fonts/@{filename}";
        src: url("@{file}.eot");

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#np-namespace {
    @color: red;
    .mixin() {
        color: @color;
    }
}

#namespace() {
    @color: blue;
    .np-mixin {

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// Dynamically generated classes as mixins:

.generate-1(@name) {
    .@{name} { 
        color: red;
    }
}

.generate-2(@name) {
    @{name} {

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.usage {
    .absolute(top 123px, left 321px);
    .relative(top, left 123px, right 456px);
    .fixed(bottom, left);

    // or whatever else CSS [property value(s)] pairs (empty value expanded as 0):
    .expand-style(padding);
    .expand-style(color red, background-color blue, border 1px solid green);
    // etc.

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.button-link {
    &, &:hover {
        color:      black;
        background: white;
    }
}

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.button-link {
    .imlazyandherearemycolors(white, black);
}

.not-button-link {
    .imlazyandherearemycolors(red, blue);
}

.imlazyandherearemycolors(@fore, @back: (#fff - @fore), @state: ~':hover') {
    color:      @fore;

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@foobar: #69c;

.z {
    @pre:   foo;
    @post:  bar;

        @a:    "@{pre}@{post}";
        @b: ~"@{@{pre}@{post}}";
  .-() {@c: ~"@{@{pre}@{post}}"} .-;

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.generate-something(4);

.generate-something(@i) when (@i > 0) {
    // just invoke next iteration *before* styles
    // so the styles output when the loop is unwinded
    // and the whole thing works in reverse:
    .generate-something((@i - 1));
    .something-@{i} {
        left: (@i * 1%);
    }

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@font-awesome-icons:
    glass "\f000",
    music "\f001",
    search "\f002",
    envelope-o "\f003",
    heart "\f004",
    star "\f005",
    star-o "\f006",
    user "\f007",