For base types, rather than a set of specific data types which is limited, how about having a standard way to indicate a type and data, like "number:12" and "ra

For base types, rather than a set of specific data types which is limited, how about having a standard way to indicate a type and data, like "number:12" and "rational:12/17" and "string:foo" and "date:2017-10-20" and "bitmap-hex:cafebabea2b9c0..."? Then let the reader parse it however they want given their desired interpretation of the type tag. There could be a base set of standard types and ideally an organizational process to add more standard types -- like mimetypes. Mimetypes also might be considered included by default perhaps like "application/json; charset=utf-8:[1, 2, 3]"). It is more characters to include a type for each primitive, but it is more expandable. Likely these files will mostly be generated and read by code anyway, with humans just looking at them now and then for debugging. If that string version seems too cluttery, another option is something like: rational:12/17 and string:foo and string:"this has spaces". Or given possible confusion with maps and colons, another option is rational/12/17 and string/foo and string/"this has spaces" and complex/−1+3i and real:30.564 and "application/json; charset=utf-8"/[1,2,3] and maybe even xml/<foo>bar\ baz</foo> and javascript/console.log("hello") and so on. Or maybe pipes? Like: rational|12/17 and string|foo and string|"this has spaces" and complex|−1+3i and real|30.564 and "application/json; charset=utf-8"|[1,2,3] and maybe even xml|<foo>bar\ baz</foo> and javascript|console.log("hello") and so on.