Official documentation
browser-compat-data data guidelines (README)
MDN Web Docs (Mozilla), GitHub, 2026
Read the originalRead on October 17, 2026
- What it is
- The rules that contributors follow when they write MDN's compatibility data. It defines what the value preview means in a version field.
- How much weight it carries
- The official guidelines for the project that publishes the compatibility data. The rules describe how the data is written, not what each browser ships, so they must be read with the browser entries.
Facts taken from this source
- MDN's data guidelines use the value preview when a browser's future stable version number is unknown or uncertain.
“when the future stable version number is unknown or uncertain” (Choosing preview values)