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+////
+/// Harmony.
+///
+/// Contains functions to make a design appear more harmonic.
+///
+/// @group Harmony
+///
+/// @access public
+////
+
+/// 
+/// Adjust a value to a modular scale.
+///
+/// For a more sophisticated solution, check out [modularscale-sass](https://github.com/modularscale/modularscale-sass).
+///
+/// @link http://alistapart.com/article/more-meaningful-typography An article about modular scales by Tim Brown
+///
+/// @param {number}        $times - Number of iterations. If positive, $base will be multiplied with $ratio. If negative, $base will be divided by $ratio.
+/// @param {number | list} $base  - Single base value or, for a multi-stranded modular scale, a list of base values
+/// @param {number}        $ratio - Ratio
+///
+/// @return {number}
+///
+@function iro-harmony-modular-scale($times, $base, $ratio) {
+    @if type-of($base) == number {
+        @return $base * iro-math-pow($ratio, $times);
+    }
+
+    $main-base:  nth($base, 1);
+    $norm-bases: ();
+
+    @each $b in iro-list-slice($base, 2) {
+        @if $b > $main-base {
+            @while $b > $main-base {
+                $b: $b / $ratio;
+            }
+            $b: $b * $ratio;
+        } @else if $b < $main-base {
+            @while $b < $main-base {
+                $b: $b * $ratio;
+            }
+        }
+
+        $norm-bases: append($norm-bases, $b);
+    }
+
+    $all-bases: append($norm-bases, $main-base);
+    $all-bases: iro-quicksort($all-bases);
+
+    $base-index: $times % length($all-bases) + 1;
+    $exp:        floor($times / length($all-bases));
+
+    @return nth($all-bases, $base-index) * iro-math-pow($ratio, $exp);
+}
+
+///
+/// Combine responsive properties with modular scales to achieve responsive modular scales.
+///
+/// @param {string | list} $props          - Property or list of properties to set
+/// @param {number}        $times          - Number of iterations. See iro-harmony-modular-scale for more information.
+/// @param {number}        $responsive-map - A map with keys = viewports and values = modular scales
+/// @param {bool}          $fluid [true]   - If enabled, property values will smoothly transition from one viewport to the next
+///
+/// @see {function} iro-harmony-modular-scale
+///
+/// @example scss - Responsive font sizes between 2 viewports based on modular scales
+///   $ms: (
+///     320px: (1rem 2rem, 1.1),
+///     640px: (1rem 2rem, 1.2)
+///   );
+///
+///   h1 {
+///     @include iro-responsive-modular-scale(font-size, 3, $ms);
+///   }
+///
+///   h2 {
+///     @include iro-responsive-modular-scale(font-size, 2, $ms);
+///   }
+///
+///   h3 {
+///     @include iro-responsive-modular-scale(font-size, 1, $ms);
+///   }
+///
+@mixin iro-responsive-modular-scale($props, $times, $responsive-map, $fluid: true) {
+    $new-map: ();
+
+    @each $key, $value in $responsive-map {
+        $new-map: map-merge($new-map, (
+                $key: iro-harmony-modular-scale($times, $value...)
+        ));
+    }
+
+    @include iro-responsive-property($props, $new-map, $fluid);
+}