W3C CSS2 Cascading Style Sheets, level 2 - instructional media + ...

9.2 Controlling box generation
The following sections describe the types of boxes that may be generated in
CSS2. A box’s type affects, in part, its behavior in the visual formatting model.
The ’display’ property, described below, specifies a box’s type.
9.2.1 Block-level elements and block boxes
Block-level elements are those elements of the source document that are formatted
visually as blocks (e.g., paragraphs). Several values of the ’display’ property
make an element block-level: ’block’, ’list-item’, ’compact’ and ’run-in’ (part of the
time; see compact [p. 99] and run-in boxes [p. 100] ), and ’table’.
Block-level elements generate a principal block box that only contains block
boxes. The principal block box establishes the containing block [p. 96] for
descendant boxes and generated content and is also the box involved in any
positioning scheme. Principal block boxes participate in a block formatting
context [p. 105] .
Some block-level elements generate additional boxes outside of the principal
box: ’list-item’ elements and those with markers [p. 164] . These additional boxes
are placed with respect to the principal box.
Anonymous block boxes
In a document like this:
Some text
More text
(and assuming the DIV and the P both have ’display: block’), the DIV appears to
have both inline content and block content. To make it easier to define the
formatting, we assume that there is an anonymous block box around "Some
text".
DIV box
anonymous box
Some text
More text
P box
Diagram showing the three boxes, of which one is anonymous, for the example
above.
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