Added placeholders for "Mixins as Functions", "Recursive Mixins / Loops"

content/features/mixins-as-functions.md

@@ -0,0 +1,46 @@
+## Using Mixins as Functions
+
+All variables defined in a mixin are visible and can be used in caller's scope (unless the caller defines its own variable with the same name). 
+
+Example:
+```less
+.mixin() {
+  @width:  100%;
+  @height: 200px;
+}
+
+.caller {
+  .mixin();
+  width:  @width;
+  height: @height;
+}
+
+```
+Output:
+```css
+.caller {
+  width:  100%;
+  height: 200px;
+}
+```
+
+Thus variables defined in a mixin can act as its return values. This allows us to create a mixin that can be used almost like a function.
+
+Example:
+```less
+.average(@x, @y) {
+  @average: ((@x + @y) / 2);
+}
+
+div {
+  .average(16px, 50px); // "call" the mixin
+  padding: @average;    // use its "return" value
+}
+
+```
+Output:
+```css
+div {
+  padding: 33px;
+}
+```

content/features/mixins-recursive-loops.md

@@ -0,0 +1,57 @@
+## Recursive Mixin ~~Calls~~ and Loops
+
+...
+
+~~It's not so easy to invent a very simple and in the same time less or more practical loop example. The simplest loops are totally useless and practical code is usually too advanced as it also uses many other (or at least one more) LESS features.~~
+
+Example:
+```less
+.loop(@index) when (@index > 0) {
+  .loop((@index - 1));    // next iteration
+  width: (10px * @index); // code for each iteration
+}
+
+div {
+  .loop(5); // launch the loop
+}
+```
+Output:
+```css
+div {
+  width: 10px;
+  width: 20px;
+  width: 30px;
+  width: 40px;
+  width: 50px;
+}
+```
+
+Example:
+```less
+@nColumns: 4;
+
+.loop(1);
+.loop(@i) when (@i <= @nColumns) {
+
+  .column-@{i} {
+    width: (@i * 100% / @nColumns)
+  }
+
+  .loop((@i + 1));
+}
+```
+Output:
+```css
+.column-1 {
+  width: 25%;
+}
+.column-2 {
+  width: 50%;
+}
+.column-3 {
+  width: 75%;
+}
+.column-4 {
+  width: 100%;
+}
+```