The first phase of the View Transitions API, explained in https://groups.google.com/a/chromium.org/g/blink-dev/c/7SMI3IklO4g/m/JS-JojxNAwAJ, allows authors to define visual transitions in SPAs (DOM state changes in the same Document). This intent is about expanding the API to support MPAs. MPA implies same-origin navigations that replace the document with another document (in the main frame or nested iframe). This is a highly requested additional feature. Examples are: https://chriscoyier.net/2022/11/08/astro-stands-to-benefit-highly-from-view-transitions/, https://adactio.com/journal/19578.
This feature allows developers to add polished visual transitions to same-origin cross-document navigations. While creating this UX is possible for DOM changes within the same Document (Single-Page App), its impossible for cross-Document navigations (Multi-Page App).
Explainers: https://github.com/WICG/view-transitions/blob/main/explainer.md#cross-document-same-origin-transitions