A CSS number is either an integer or "zero or more digits followed by a dot (.) followed by one or more digits". 5.0000000000000005e-12px is invalid, and I'm not sure we want everyone downloading jQuery to bear the burden of additional code for normalizing extreme-valued input numbers.

The 5.0000000000000005e-12 is a valid floating point value in javascript, by simply adding "px" jquery creates invalid string "5.0000000000000005e-12px" and then tries to pass it to CSS.

I understand that. What I don't understand (but am willing to listen to arguments on) is why the changes (and additional size and performance hit and ongoing maintenance) required to specify CSS values with more precision than would ever be noticed should live within jQuery instead of in more special-purpose code.

The issue is not about precision, but about ignoring the assignments.

Assume a code which does some calculations and returns an object containing left,top,width,height and something else, then assume that the left value is something like 5.000e-12 it should have been 0 but due to divisions, sqrt whatever it isn't exactly 0. In this case if you pass this object to jquery it will assign top,width,height but will skip left (this is what exactly happened to me). If jquery is going to stay with this issue then we should agree with the this note "Don't pass any variable to jquery without formatting it, or without forcing lower precision or you will get unexpected behavior".

BTW: People may think that the following code outputs 0.

console.log(-1 + 1.15 - 0.15);

http://jsfiddle.net/Z8KcL/

But unfortunately no, it outputs something like -8.326672684688674e-17 in most of browsers. This is well know issue of floating point type.

And if you pass this to jquery it will just ignore that.

+84 bytes to dist/jquery.min.js and it doesn't even work consistently in all browsers: https://github.com/gibson042/jquery/compare/jquery:d8576139...14494

I recommend normalizing extreme values intended for CSS properties.