Faster animation & commit docs.

assets/stylesheets/_animations.scss

@@ -7,7 +7,7 @@
 	animation-fill-mode: forwards;
 }
 
-@mixin components-popover__appear-animation($speed: 0.2s, $delay: 0s) {
+@mixin components-popover__appear-animation($speed: 0.1s, $delay: 0s) {
 	animation: components-popover__appear-animation $speed cubic-bezier(0, 0, 0.2, 1) $delay;
 	animation-fill-mode: forwards;
 }

docs/designers-developers/designers/animation.md

@@ -0,0 +1,69 @@
+# Animation
+
+Animation can help reinforce a sense of hierarchy and spatial orientation. This documents goes into principles you should follow when you add animation.
+
+## Principles
+
+### Point of Origin
+
+- Animation can help anchor an interface element. For example a menu can scale up from the button that opened it.
+- Animation can help give a sense of place; for example a sidebar can animate in from the side, implying it was always hidden off-screen.
+- Design your animations as if you're working with real-world materials. Imagine your user interface elements are made real materials — when not on screen, where are they? User animation to help express that.
+
+### Speed
+
+- Animations should never block a user interaction. The should be fast, almost always complete in less than 0.2 seconds.
+- A user should not have to wait for an animation to finish before they can interact.
+- Animations should be performant. Use `transform` CSS properties when you can, these render elements on the GPU making them smooth. 
+- If an animation can't be made fast & performant, leave it out.
+
+### Simple
+
+- Don't bounce if the material isn't made of rubber.
+- Don't rotate, fold, or animate on a curve. Keep it simple.
+
+### Consistency
+
+In creating consistent animations, we have to establish physical rules for how elements behave when animated. When all animations follow these rules, they feel consistent, related, and predictable. An animation should match user expectations, if it doesn't, it's probably not the right animation for the job.
+
+Reuse animations if one already exists for your task. 
+
+## Inventory, Reused animations
+
+The following is a running list of existing animations, and how they fit with the above principles. 
+
+### `edit-post__loading-fade-animation`
+
+This is a "pulsing fade" animation that is used when an element is _transient_. For example when an image is being uploaded. It is simple, and indicates background work.
+
+### `edit-post__fade-in-animation`
+
+This is the most basic fade in animation. It simply fades from transparent to opaque.
+
+### `components-popover__appear-animation`
+
+This animation is meant for popover content, such as menus appearing. It shows the popover scaling from 0 to full size, from its point of origin. Be sure to combine it with the correct point of origin. For example the Block Library opens down and to the right, which means it needs a `transform-origin: top left;` to scale diagonally from the top left corner.
+
+### `components-button__busy-animation`
+
+When a button is working, there's a set of diagonal stripes that animate from left to right. 
+
+### `components-modal__appear-animation`
+
+Modal windows are cards that live below the viewport. When invoked, they animate in fro the button and upwards. Because of their relative size, this is a brief animation that includes a fade. 
+
+### `components-spinner__animation`
+
+This is a simple rotation used for a loading-state spinner.
+
+### `edit-post-fullscreen-mode__slide-in-animation`
+
+When you enter fullscreen mode, the editor bar animates downwards from the top.
+
+### `edit-post-layout__slide-in-animation`
+
+The Publish sidebar lives to the right of the viewport, and when you press the Publish... button, it slides in from the right.
+
+### `nux-pulse`
+
+This animation is used for the dot indicators that appear in the out of box experience. They create a "pulsing" effect behind the dot indicators.