Merge branch 'twbs/v4-dev' into dropdown-keyboard

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diff --git a/docs/utilities/sizing.md b/docs/utilities/sizing.md
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+---
+layout: docs
+title: Sizing
+group: utilities
+---
+
+Easily make an element as wide or as tall (relative to its parent) with our width and height utilities. Includes support for `25%`, `50%`, `75%`, and `100%` by default.
+
+Width and height utilities are generated from the `$sizes` Sass map in `_variables.scss`. Modify those values as you need to generate different utilities here.
+
+{% example html %}
+<div class="w-25 p-3" style="background-color: #eee;">Width 25%</div>
+<div class="w-50 p-3" style="background-color: #eee;">Width 50%</div>
+<div class="w-75 p-3" style="background-color: #eee;">Width 75%</div>
+<div class="w-100 p-3" style="background-color: #eee;">Width 100%</div>
+{% endexample %}
+
+{% example html %}
+<div style="height: 100px; background-color: rgba(255,0,0,0.1);">
+  <div class="h-25 d-inline-block" style="width: 120px; background-color: rgba(0,0,255,.1)">Height 25%</div>
+  <div class="h-50 d-inline-block" style="width: 120px; background-color: rgba(0,0,255,.1)">Height 50%</div>
+  <div class="h-75 d-inline-block" style="width: 120px; background-color: rgba(0,0,255,.1)">Height 75%</div>
+  <div class="h-100 d-inline-block" style="width: 120px; background-color: rgba(0,0,255,.1)">Height 100%</div>
+</div>
+{% endexample %}
+
+You can also use `max-width: 100%;` and `max-height: 100%;` utilities as needed.
+
+{% example html %}
+<img class="mw-100" data-src="holder.js/1000px100?text=Max-width%20%3D%20100%25" alt="Max-width 100%">
+{% endexample %}
+
+{% example html %}
+<div style="height: 100px; background-color: rgba(255,0,0,0.1);">
+  <div class="mh-100" style="width: 100px; height: 200px; background-color: rgba(0,0,255,0.1);">Max-height 100%</div>
+</div>
+{% endexample %}