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Generally, the content of a block box is confined to the content edges of the box. In certain cases, a box may overflow, meaning its content lies partly or entirely outside of the box, e.g.:
Whenever overflow occurs, the 'overflow' property specifies
how (and whether)whether a box is clipped. The 'clip' property specifies the sizeclipped to its content box, and shape of the clipping region. Specifyingif so, whether
a small clipping region may cause clipping of otherwise visible contents.scrolling mechanism is provided to access any clipped out content.
Value: | visible | hidden | scroll | auto | inherit |
Initial: | visible |
Applies to: | block-level and replaced elements |
Inherited: | no |
Percentages: | N/A |
Media: | visual |
Computed value: | as specified |
This property specifies whether the content of a block-level element is clipped when it overflows the element's box (which is acting as a containing block for the content). Values have the following meanings:
Even if 'overflow' is set to 'visible', content may be clipped to a UA's document window by the native operating environment.
HTML UAs may apply the overflow property from the BODY or HTML elements to the viewport.
Consider the following example of a block quotation (BLOCKQUOTE) that is too big for its containing block (established by a DIV). Here is the source document:
<DIV> <BLOCKQUOTE> <P>I didn't like the play, but then I saw it under adverse conditions - the curtain was up.<DIVclass="attributed-to">-<CITE>- GrouchoMarx</DIV>Marx</CITE> </BLOCKQUOTE> </DIV>
Here is the style sheet controlling the sizes and style of the generated boxes:
div { width : 100px; height: 100px; border: thin solid red; } blockquote { width : 125px; height : 100px; margin-top: 50px; margin-left: 50px; border: thin dashed black }DIV.attributed-tocite { display: block; text-align : right; border: none }
The initial value of 'overflow' is 'visible', so the BLOCKQUOTE would be formatted without clipping, something like this:
[D]Setting 'overflow' to
'hidden' for the DIV element, on the other hand, causes the
BLOCKQUOTE to be clipped by the containing block:
[D]A value of 'scroll' would tell UAs that support
a visible scrolling mechanism to display one so that users
could access the clipped content.
A clipping
region defines what portion of an element's
rendered contentborder box
is visible. By default, the clipping region has the same size and shape
as the element's box(es).border box. However, the clipping region may be
modified by the 'clip' property.
The 'clip' property applies only to elements that have a 'overflow' property with a value other than 'visible'.absolutely positioned elements.
Values have the following meanings:
<top>, <right>,
<bottom>,
and <left> may
either have a <length>
value or 'auto'. Negative lengths are permitted. The value 'auto'
means that a given edge of the clipping region will be the same as the
edge of the element's generated box (i.e., 'auto' means the same as
'0'.)'0' for <top> and <left> (in left-to-right text,
<right> in right-to-left
text), the same as the computed value of the height plus the sum of
vertical padding and border widths for <bottom>, and the same as the
computed value of the width plus the sum of the horizontal padding and
border widths for <right>
(in left-to-right text, <left> in right-to-left text),
such that four 'auto' values result in the clipping region being fit
with the border edge).
When coordinates are rounded to pixel coordinates, care should be
taken that no pixels remain visible when <left> +and
<right> is equal tohave the element's widthsame value (or <top> +and <bottom>
equalshave the element's height),same value), and conversely that no pixels within the
element's box remain hidden when these values are 0.'auto'.
The element's ancestors may also have clipping regions (in case(e.g. if
their 'overflow' property is
not 'visible'); what is rendered is the intersection of the various
clipping regions.
If the clipping region exceeds the bounds of the UA's document window, content may be clipped to that window by the native operating environment.
The following two rules:
p { clip: rect(5px,10px,10px,40px, 45px, 5px); } p { clip: rect(5px,-5px,10px,55px, 45px, 5px); }
will create the rectangular clipping regions delimited by the dashed lines in the following illustrations:
[D]Note. In CSS2,CSS 2.1, all clipping
regions are rectangular. We anticipate future extensions to permit
non-rectangular clipping. Future versions may also reintroduce a
syntax for offsetting shapes from each edge instead of offsetting from
a point.
Value: | visible | hidden | collapse | inherit |
Initial: | |
Applies to: | all elements |
Inherited: | |
Percentages: | N/A |
Media: | visual |
Computed value: | as specified |
The 'visibility' property specifies whether the boxes generated by an element are rendered. Invisible boxes still affect layout (set the 'display' property to 'none' to suppress box generation altogether). Values have the following meanings:
This property may be used in conjunction with scripts to create dynamic effects.
In the following example, pressing either form button invokes a user-defined script function that causes the corresponding box to become visible and the other to be hidden. Since these boxes have the same size and position, the effect is that one replaces the other. (The script code is in a hypothetical script language. It may or may not have any effect in a CSS-capable UA.)
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"> <HTML> <HEAD> <STYLE type="text/css"> <!-- #container1 { position: absolute; top: 2in; left: 2in; width: 2in } #container2 { position: absolute; top: 2in; left: 2in; width: 2in; visibility: hidden; } --> </STYLE> </HEAD> <BODY> <P>Choose a suspect:</P> <DIV id="container1"> <IMG alt="Al Capone" width="100" height="100" src="suspect1.jpg"> <P>Name: Al Capone</P> <P>Residence: Chicago</P> </DIV> <DIV id="container2"> <IMG alt="Lucky Luciano" width="100" height="100" src="suspect2.jpg"> <P>Name: Lucky Luciano</P> <P>Residence: New York</P> </DIV> <FORM method="post" action="http://www.suspect.org/process-bums"> <P> <INPUT name="Capone" type="button" value="Capone" onclick='show("container1");hide("container2")'> <INPUT name="Luciano" type="button" value="Luciano" onclick='show("container2");hide("container1")'> </FORM> </BODY> </HTML>