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Added Element wrapping limitations to Known Issues

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Koen Kivits
2015-12-08 21:20:38 +01:00
parent aea01af17a
commit 8fd7a6c0b6
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README.md
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@@ -91,6 +91,7 @@ window.addEventListener('WebComponentsReady', function(e) {
## Known Issues
* [Limited CSS encapsulation](#encapsulation)
* [Element wrapping / unwrapping limitations](#wrapping)
* [Custom element's constructor property is unreliable](#constructor)
* [Contenteditable elements do not trigger MutationObserver](#contentedit)
* [ShadowCSS: :host-context(...):host(...) doesn't work](#hostcontext)
@@ -110,6 +111,13 @@ WebComponents.ShadowCSS.shimStyling( shadowRoot, scope );
For a full explanation on the implementation and both the possibilities and the limitations of ShadowCSS please view the documentation in the [ShadowCSS source](src/ShadowCSS/ShadowCSS.js).
### Element wrapping / unwrapping limitations <a id="wrapping"></a>
The Shadow DOM polyfill is implemented by [wrapping](http://webcomponents.org/polyfills/shadow-dom/#wrappers) DOM elements whenever possible. It does this by wrapping methods like `document.querySelector` to return wrapped DOM elements. This has a few caveats:
* Not _everything_ can be wrapped. For example, elements like `document`, `window`, `document.body`, `document.fullscreenElement` and others are non-configurable and thus cannot be overridden.
* Wrappers don't support [live NodeLists](https://developer.mozilla.org/en-US/docs/Web/API/NodeList#A_sometimes-live_collection) like `HTMLElement.childNodes` and `HTMLFormElement.elements`. All NodeLists are snapshotted upon read. See [#217](https://github.com/webcomponents/webcomponentsjs/issues/217) for an explanation.
In order to work around these limitations the polyfill provides the `ShadowDOMPolyfill.wrap` and `ShadowDOMPolyfill.unwrap` methods to respectively wrap and unwrap DOM elements manually.
### Custom element's constructor property is unreliable <a id="constructor"></a>
See [#215](https://github.com/webcomponents/webcomponentsjs/issues/215) for background.