Isolating applications hosted by plug-in code

In a computing environment, a system comprising:

• at least one processor;
• a memory communicatively coupled to the at least one processor;
• a first container executed by the at least one processor to run in a browser comprising a host application;
• a data structure associated with the first container, the data structure including a tree of elements, the tree of elements including user interface elements of the first container;
• and
• a second container instantiated by the first container within an isolation boundary that is hidden from the browser, the second container having disabled access to browser elements, other browser-hosted application elements, and elements of the first container, the second container corresponding to a host element in the tree of elements, wherein the host element defines the isolation boundary, and wherein a hosted application is presented within the host application within the isolation boundary.

One or more computer storage media having computer-executable instructions stored thereon, which in response to execution by a computer, cause the computer to perform operations comprising:

• running a first application as a first container in a browser;
• creating an element tree representing elements of the first application;
• hosting a second application within the first container, wherein hosting the second application includes:
• containing a host element for the first container in the element tree,
• instantiating a second container that is hidden from the browser and disabled from accessing data of the browser, data of the first container, and data of other browser-hosted application elements, and
• loading a second application to run in the second container, the second application providing user interface elements via the host element to the first application;
• and
• rendering visible output by processing user interface elements of the first application and user interface elements of the second application.