ui:portalContainer

Renders the content that ui:portal collected under the same name at the place where you write it.

Use it to portal content somewhere other than the end of <body>. Give the portal a custom name and place the container with that name where the content should end up:

<ui:portal name="sidebar">...</ui:portal>
...
<ui:portalContainer name="sidebar" />

The default name renders at the end of <body> through TYPO3's page rendering. Add <ui:portalContainer /> for it when you render outside that pipeline, for example in an isolated component preview.

The container also renders an empty <template data-portal-container> marker. The portals of a cloned ui:template move after it.