@# Portal The `Portal` component renders its children into a new "subtree" outside of the current component hierarchy. It is an essential piece of [`Overlay`](#core/components/overlay), responsible for ensuring that the overlay contents cover the application below. In most cases you do not need to use a `Portal` directly; this documentation is provided simply for reference. @## React 15 In a **React 15** environment, `Portal` will use `ReactDOM.unstable_renderSubtreeIntoContainer` to achieve the teleportation effect, which has a few caveats: 1. `Portal` `children` are wrapped in an extra `
` inside the portal container element. 1. Test harnesses such as `enzyme` cannot trivially find elements "through" Portals as they're not in the same React tree. 1. React `context` _is_ preserved (this one's a good thing). In a **React 16+** environment, the `Portal` component will use [`ReactDOM.createPortal`](https://reactjs.org/docs/portals.html) which preserves the React tree perfectly and does not require any of the above caveats. @## React context `Portal` supports the following options on its [React context](https://facebook.github.io/react/docs/context.html). To use them, supply a child context to a subtree that contains the Portals you want to customize.
Blueprint uses the React 15-compatible `getChildContext()` API instead of the newer React 16.3 `React.createContext()` API.
@interface IPortalContext @## Props The `Portal` component functions like a declarative `appendChild()`, or jQuery's `$.fn.appendTo()`. The children of a `Portal` component are inserted into a new child of the ``. `Portal` is used inside [`Overlay`](#core/components/overlay) to actually overlay the content on the application.

A note about responsive layouts

For a single-page app, if the `` is styled with `width: 100%` and `height: 100%`, a `Portal` may take up extra whitespace and cause the window to undesirably scroll. To fix this, instead apply `position: absolute` to the `` tag.
@interface IPortalProps