Drop .center-block for .m-x-auto

- Both classes do about the same thing, but with different names
- Clarifies docs for .m-x-auto requiring a fixed width block element for it to work
- Add missing heading for clearfix section in docs (unrelated)

1 files changed, 13 insertions, 22 deletions

diff --git a/docs/components/utilities.md b/docs/components/utilities.md
index 00bc96721..e59869fcd 100644
--- a/docs/components/utilities.md
+++ b/docs/components/utilities.md
@@ -60,8 +60,19 @@ Here are some representative examples of these classes:
 }
 {% endhighlight %}
 
-Additionally, Bootstrap also includes an `.m-x-auto` class which sets the horizontal margins to `auto`.
+Additionally, Bootstrap also includes an `.m-x-auto` class for centering fixed-width block level content by setting the horizontal margins to `auto`.
 
+<div class="bd-example">
+  <div class="m-x-auto" style="width: 200px; background-color: rgba(86,61,124,.15);">
+    Centered element
+  </div>
+</div>
+
+{% highlight html %}
+<div class="m-x-auto" style="width: 200px;"">
+  Centered element
+</div>
+{% endhighlight %}
 
 ## Text alignment
 
@@ -191,27 +202,7 @@ Two similar non-responsive mixins (`pull-left` and `pull-right`) are also availa
 }
 {% endhighlight %}
 
-## Center content
-
-Set an element to `display: block;` and center via `margin`. Available as a mixin and class.
-
-{% example html %}
-<div class="center-block">Centered block</div>
-{% endexample %}
-
-{% highlight scss %}
-// Class
-.center-block {
-  display: block;
-  margin-left: auto;
-  margin-right: auto;
-}
-
-// Usage as a mixin
-.element {
-  @include center-block;
-}
-{% endhighlight %}
+## Clearfix
 
 Easily clear `float`s by adding `.clearfix` **to the parent element**. Utilizes [the micro clearfix](http://nicolasgallagher.com/micro-clearfix-hack/) as popularized by Nicolas Gallagher. Can also be used as a mixin.