Currently, the //| mill-version: value syntax has a lot of limitations:

• It must be on the first line of the build header
• mill-version must be unquoted
• value must be unquoted
• There can be no YAML comments or anything after the value

These limitations come from the necessity to parse this line in the ./mill and ./mill.bat bootstrap scripts, but they are very restrictive. While we cannot hope to parse the entirety of YAML in bash and bat code, we should try making the scripts a bit smarter to loosen these restrictions:

• Allow //| mill-version on any line of the build header
• Allow mill-version and value to be quoted by single or double quotes
• Allow YAML comments to be placed after the build header