title: Possible to substitute mixins used inside other mixins?
body: <p>I have some Less mixins I use to create a site navigation, which is mostly the same in every project.</p>
  
  <p>I've made it editable through global variables, but these get long and ungainly for nested elements. For example:</p>
  
  <pre><code>@nav-main-sub-menu-item-title-text-transform: uppercase;
  </code></pre>
  
  <p>It would be really nice if I could disable a specific nested mixin, and re-instantiate it manually.</p>
  
  <pre><code>// Main nav
  
  .Nav() {
  
    .nav {
  
      display:block;
  
      &amp; when (@Nav-Item = default) {
        .Nav-Item();
      }
  
      // Would be nice to insert a custom .Nav-Item() here
      // when @Nav-Item is set to 'custom'
  
    }
  
  }
  
  .Nav();
  
  // Enables Nav-Item
  
  @Nav-Item: default;
  
  // Nav item
  
  .Nav-Item(@color: red) {
  
    .item {
  
      color: @color;
  
    }
  
  }
  
  // Override 
  
  @Nav-Item: custom;
  
  .Nav-Item(@color: blue);
  </code></pre>
  
  <p>I could add '.nav' into the item mixin itself to make it more self-encapsulated, but this goes against the "don't repeat yourself" mantra... </p>
  
  <p>Plus, media queries, etc, make things more complicated than just this simple example.</p>
  
  <pre><code>.Nav-Item(@color: red) {
  
    .nav {
  
      .item {
  
        color: @color;
  
      }
  
    }
  
  }
  </code></pre>
  
  <p>I don't know if there's a good solution, but I just figured I'd put this out there.</p>