Want to know more about Flex-Layout flex-start instead of start information?

[richex-cn]

The following warning is often encountered during development:

autoprefixer: start value has mixed support, consider using flex-start instead

I want to find out why start / end is not recommended? What does this multiple support specifically mean?

Unfortunately, I looked around and didn't explain in detail, Here are some related contents:

postcss/autoprefixer#1291
https://github.com/mozilla/addons-frontend/issues/7312
https://github.com/anc95/postcss-flex-value