Ryan Johnson

## ES5 Adapter * needed to convert ES5 logic to ES6 class syntax for custom element registration * requires hacks and redundant logic to function outside of HTML imports *...

## Limited CSS Layout Capabilities * Flexbox instead of Modern CSS Grid * Flexbox is not intended for 2D layout (hacks are in place to make it behave better, but...

## Legacy CSS Grid instead of Flexbox * In cases where we need to implement scrollbars along a single dimension (horizontally or vertically) on elements that have fluid dimensions up...

## Broken implementation of valid semantic HTML5 elements * For unknown elements, browsers will style them as inline elements. This is problematic when you want to use valid semantic HTML5...

## Platform Polyfills * Based on [research around required polyfills](https://github.com/rackerlabs/helix-ui/blob/master/src/COMPATIBILITY.md), IE is the only browser that needs additional platform polyfills beyond what `webcomponentsjs` provides. * Maintaining polyfills adds development overhead....

## Limited Support for CSS Custom Properties The ShadyCSS polyfill that's included with `webcomponentsjs` will detect if a CSS custom property is consumed in the Shadow DOM and will stamp...

## ShadyDOM Rewrites - CSS Styling Conflicts ShadyDOM doesn't prevent Light DOM CSS from accidentally styling ShadyDOM markup. _Note: this isn't IE-specific, but it will eventually become an exclusive problem...

## ShadyDOM Rewrites - Differing CSS Selectors in Light DOM ShadyDOM modifies the generated DOM to the point of requiring two different CSS selectors in order to target the same...

## `window.opener` API exploits External links to untrusted URLs can fall victim to exploits in the `window.opener` API. You can view a safe demonstration of how this could be used...

### `min-height`/`min-width` affects Drag and Drop events Details: TBD