Rearrange all the docs to allow for a docs/major.minor/ setup

docs/4.0/utilities/responsive-helpers.md

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+---
+layout: docs
+title: Responsive helpers
+description: Create responsive video or slideshow embeds based on the width of the parent by creating an intrinsic ratio that scales on any device.
+group: utilities
+toc: true
+---
+
+## Responsive embeds
+
+Rules are directly applied to `<iframe>`, `<embed>`, `<video>`, and `<object>` elements; optionally use an explicit descendant class `.embed-responsive-item` when you want to match the styling for other attributes.
+
+**Pro-Tip!** You don't need to include `frameborder="0"` in your `<iframe>`s as we override that for you.
+
+{% example html %}
+<div class="embed-responsive embed-responsive-16by9">
+  <iframe class="embed-responsive-item" src="https://www.youtube.com/embed/zpOULjyy-n8?rel=0" allowfullscreen></iframe>
+</div>
+{% endexample %}
+
+Aspect ratios can be customized with modifier classes.
+
+{% highlight html %}
+<!-- 21:9 aspect ratio -->
+<div class="embed-responsive embed-responsive-21by9">
+  <iframe class="embed-responsive-item" src="..."></iframe>
+</div>
+
+<!-- 16:9 aspect ratio -->
+<div class="embed-responsive embed-responsive-16by9">
+  <iframe class="embed-responsive-item" src="..."></iframe>
+</div>
+
+<!-- 4:3 aspect ratio -->
+<div class="embed-responsive embed-responsive-4by3">
+  <iframe class="embed-responsive-item" src="..."></iframe>
+</div>
+
+<!-- 1:1 aspect ratio -->
+<div class="embed-responsive embed-responsive-1by1">
+  <iframe class="embed-responsive-item" src="..."></iframe>
+</div>
+{% endhighlight %}
+
+## Responsive floats
+
+These utility classes float an element to the left or right, or disable floating, based on the current viewport size using the [CSS `float` property](https://developer.mozilla.org/en-US/docs/Web/CSS/float). `!important` is included to avoid specificity issues. These use the same viewport width breakpoints as the grid system.
+
+Two similar non-responsive Sass mixins (`float-left` and `float-right`) are also available.
+
+{% example html %}
+<div class="float-left">Float left on all viewport sizes</div><br>
+<div class="float-right">Float right on all viewport sizes</div><br>
+<div class="float-none">Don't float on all viewport sizes</div><br>
+
+<div class="float-sm-left">Float left on viewports sized SM (small) or wider</div><br>
+<div class="float-md-left">Float left on viewports sized MD (medium) or wider</div><br>
+<div class="float-lg-left">Float left on viewports sized LG (large) or wider</div><br>
+<div class="float-xl-left">Float left on viewports sized XL (extra-large) or wider</div><br>
+{% endexample %}
+
+{% highlight scss %}
+// Related simple non-responsive mixins
+.element {
+  @include float-left;
+}
+.another-element {
+  @include float-right;
+}
+{% endhighlight %}