Merge branch 'docs-fe-html' into 'master'

Add HTML style guide

See merge request gitlab-org/gitlab-ce!17616

doc/development/new_fe_guide/style/html.md

 # HTML style guide
 
-> TODO: Add content
+## Buttons
+
+<a name="button-type"></a><a name="1.1"></a>
+- [1.1](#button-type) **Use button type** Button tags requires a `type` attribute according to the [W3C HTML specification][button-type-spec].
+
+```
+// bad
+<button></button>
+
+// good
+<button type="button"></button>
+```
+
+<a name="button-role"></a><a name="1.2"></a>
+- [1.2](#button-role) **Use button role for non buttons** If an HTML element has an onClick handler but is not a button, it should have `role="button"`. This is more [accessible][button-role-accessible].
+
+```
+// bad
+<div onClick="doSomething"></div>
+
+// good
+<div role="button" onClick="doSomething"></div>
+```
+
+## Links
+
+<a name="blank-links"></a><a name="2.1"></a>
+- [2.1](#blank-links) **Use rel for target blank** Use `rel="noopener noreferrer"` whenever your links open in a new window i.e. `target="_blank"`. This prevents [the following][jitbit-target-blank] security vulnerability documented by JitBit
+
+```
+// bad
+<a href="url" target="_blank"></a>
+
+// good
+<a href="url" target="_blank" rel="noopener noreferrer"></a>
+```
+
+<a name="fake-links"></a><a name="2.2"></a>
+- [2.2](#fake-links) **Do not use fake links** Use a button tag if a link only invokes JavaScript click event handlers. This is more semantic.
+
+```
+// bad
+<a class="js-do-something" href="#"></a>
+
+// good
+<button class="js-do-something" type="button"></button>
+```
+
+[button-type-spec]: https://www.w3.org/TR/2011/WD-html5-20110525/the-button-element.html#dom-button-type
+[button-role-accessible]: https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/ARIA_Techniques/Using_the_button_role
+[jitbit-target-blank]: https://www.jitbit.com/alexblog/256-targetblank---the-most-underestimated-vulnerability-ever/