docs

Description of Problem The scoped CSS tips currently say an element selector such as will be "many times slower" when scoped. That warning is directionally useful, but it reads more absolute than current browser behavior warrants and does not tell readers when they should actually care. Addresses vuejs/core#2608. Proposed Solution This updates the tip to explain what scoped CSS compiles to, notes that selector cost depends on the browser, selector, and affected DOM size, and keeps the practical guidance to prefer classes or ids in large or frequently updated component trees. Additional Information Validation: This is a docs-only wording change, so I did not run the full VitePress site build.

Summary clarify that applies once per listener attachment explain that the listener is removed after the first invocation note that recreating the element or child component attaches a fresh listener Closes #3033 Note This PR supersedes #3423, which I had to close after the original fork relationship was broken during repo visibility changes on my side. The content is being resubmitted unchanged from a proper public fork.

Summary clarify that must be registered before the first in an async watcher callback add a small async example showing the intended usage pattern keep the guidance next to the existing alternative Closes #3222 Note This PR supersedes #3422, which I had to close after the original fork relationship was broken during repo visibility changes on my side. The content is being resubmitted unchanged from a proper public fork.