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

auto
The width depends on the values of other properties. See the sections
below.
Negative values for ’width’ are illegal.
Example(s):
For example, the following rule fixes the content width of paragraphs at 100
pixels:
P { width: 100px }
10.3 Computing widths and margins
The computed values of an element’s ’width’, ’margin-left’, ’margin-right’, ’left’
and ’right’ properties depend on the type of box generated and on each other. In
principle, the computed values are the same as the specified values, with ’auto’
replaced by some suitable value, but there are exceptions. The following situations
need to be distinguished:
1. inline, non-replaced elements
2. inline, replaced elements
3. block-level, non-replaced elements in normal flow
4. block-level, replaced elements in normal flow
5. floating, non-replaced elements
6. floating, replaced elements
7. absolutely positioned, non-replaced elements
8. absolutely positioned, replaced elements
Points 1-6 include relative positioning.
10.3.1 Inline, non-replaced elements
The ’width’ property does not apply. A specified value of ’auto’ for ’left’, ’right’,
’margin-left’ or ’margin-right’ becomes a computed value of ’0’.
10.3.2 Inline, replaced elements
A specified value of ’auto’ for ’left’, ’right’, ’margin-left’ or ’margin-right’ becomes a
computed value of ’0’. A specified value of ’auto’ for ’width’ gives the element’s
intrinsic [p. 30] width as the computed value.
10.3.3 Block-level, non-replaced elements in normal
flow
If ’left’ or ’right’ are given as ’auto’, their computed value is 0. The following
constraints must hold between the other properties:
’margin-left’ + ’border-left-width’ + ’padding-left’ + ’width’ + ’padding-right’ +
’border-right-width’ + ’margin-right’ = width of containing block [p. 131]
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