This StackOverflow replay happens to answer this question exactly, the actual definition of "CFWS" is near the bottom of the text: https://stackoverflow.com/a/

This StackOverflow replay happens to answer this question exactly, the actual definition of "CFWS" is near the bottom of the text: https://stackoverflow.com/a/42193413/544779 https://stackoverflow.com/a/42193413/544779 It's just an excerpt of the spec, but I link to it instead of to the spec because I think it's easier to read (formatting/colors) and it has links to the spec anyway.