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CSS gurus have known for a long time that when IE/Win sees that a box has a stated dimension that is not large enough to enclose the content of that box, the browser will wrongly enlarge the width of the box to accommodate unbreakable lines, such as long URLs. IE/Win will also extend the height of a box so that its content does not overflow the bottom border of the box. Browsers that more closely follow the W3C specifications let the extra content protrude beyond the height or width controlled box.
Voor de volledigheid de W3C specificaties er maar even bij gezocht:
Citaat:
9.1.2 Containing blocks
In CSS2, many box positions and sizes are calculated with respect to the edges of a rectangular box called a containing block. In general, generated boxes act as containing blocks for descendant boxes; we say that a box "establishes" the containing block for its descendants. The phrase "a box's containing block" means "the containing block in which the box lives," not the one it generates.
Each box is given a position with respect to its containing block, but it is not confined by this containing block; it may overflow.
The root of the document tree generates a box that serves as the initial containing block for subsequent layout.
The width of the initial containing block may be specified with the 'width' property for the root element. If this property has the value 'auto', the user agent supplies the initial width (e.g., the user agent uses the current width of the viewport).
The height of the initial containing block may be specified with the 'height' property for the root element. If this property has the value 'auto', the containing block height will grow to accommodate the document's content.
The initial containing block cannot be positioned or floated (i.e., user agents ignore the 'position' and 'float' properties for the root element).
The details of how a containing block's dimensions are calculated are described in the next chapter.
bron: