A component can finish its work before the browser starts
This paragraph began as Markdown in a local file. A Server Component read the file, converted it into HTML, and supplied the rendered preview as children to an interactive Client Component.
The browser receives the content and the toggle's JavaScript. It does not need the filesystem reader, Markdown parser, or HTML sanitizer to render this preview.
Changing this file requires another build. Clicking Hide details does not: that interaction belongs to the browser.