History of in operator

clear review; thanks!

I came to this page looking to find the distinction between the use of the `in` keyword when used in a for loop versus a conditional statement. I believe adding a link to the `for...in` article under the "See also" section would be very helpful.

fix compat parsing error

I don't know how to indicate supported versions, but I do know that symbols work as the left operands, and that even odd values for the left operand, like null, booleans, and objects, are converted to strings.

add ES draft

add Reflect.has

Replaced static text for specification by macros

lint