When the getAvailability() method is called, the user agent MUST run the following steps:

Input

presentationUrls, a list of presentation request URLs

Output

P, a Promise

1. If one of the following conditions is true:
   • The result of running the prohibits mixed security contexts algorithm on the document's settings object is "Prohibits Mixed Security Contexts" and presentationUrl is an a priori unauthenticated URL.
   • The document object's active sandboxing flag set has the sandboxed presentation browsing context flag set.
   Run the following substeps:
   1. Return a Promise rejected with a SecurityError DOMException.
   2. Abort these steps.
2. Let P be a new Promise.
3. Return P, but continue running these steps in parallel.
4. If the user agent is unable to monitor the list of available presentation displays for the entire duration of the controlling browsing context (e.g., because the user has disabled this feature), then:
   1. Resolve P with a new PresentationAvailability object with its value property set to false.
   2. Abort all the remaining steps.
5. If the user agent is unable to continuously monitor the list of available presentation displays but can find presentation displays in order to start a connection, then:
   1. Reject P with a NotSupportedError DOMException.
   2. Abort all the remaining steps.
6. If there exists a tuple (A, presentationUrls) in the set of availability objects, then:
   1. Resolve P with A.
   2. Abort all the remaining steps.
7. Let A be a new PresentationAvailability object with its value property set as follows:
   1. false if the list of available presentation displays is empty.
   2. true if there is at least one compatible presentation display for some member of presentationUrls. Meaning there is an entry (presentationUrl, display) in the list of available presentation displays for some presentationUrl in presentationUrls.
   3. false otherwise.
8. Create a tuple (A, presentationUrls) and add it to the set of availability objects.
9. Run the algorithm to monitor the list of available presentation displays.
10. Resolve P with A.