CSS3 box-sizing: margin-box; Why not?

Question

Why don\'t we have box-sizing: margin-box;? Usually when we put box-sizing: border-box; in our style sheets we really mean the former.

Answer 1

There interesting situation when using box-sizing inside body content

no content no border box gives no any value on left-right margin % recount of this two box recount algoritms

  .body{
    box-sizing: border-box;
    margin:0 3%;
  }

Firefox versions before 57 also supported the padding-box value for box-sizing, though this value was been removed from the specification and later versions of the browser.

So margin-box even not planned...