What's the relationship between margin, padding and width in different browsers?

Question

CSS width value = display width of inside?

or

CSS width value = display width of inside + CSS margin-left + CSS margin-right?

Answer 1

It not only depends from the browser and version you choose, but also from the doctype of your html document. Internet explorer in "quirks mode" is for example completely different from Internet explorer with doctype XHTML 1.0 Transitional.