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Issue 158 proposed text

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Thu, 3 Jun 2010 16:51:13 -0700
Message-ID: <AANLkTilgwfgdQr36zRXnETqMt1fe1YFDo90k8XedPL3P@mail.gmail.com>
To: www-style list <www-style@w3.org>
This is meant to resolve issue 158: http://wiki.csswg.org/spec/css2.1#issue-158

In this issue, Anton Prowse points out that the phrasing in section
9.5.2 is confusing.  Specifically, the phrase "these margins" is used
to refer to margins mentioned two paragraphs previous, when there is
at least one other margin mentioned between those two points.  This is
an attempted rewrite of this section to resolve the ambiguity and make
the entire clearance section clearer.

Delete the text in 9.5.2 from "Computing the clearance on an
element..." to the end of the note after the bulleted list.  Replace
it with this text:

"""
Computing the clearance of an element on which 'clear' is set is done
by first determining the hypothetical position of the element's top
border edge within its parent block.  When computing this position,
collapse all appropriate margins.

If the top border edge of the cleared element at this hypothetical
position is flush with or below the bottom outer edge of the lowest
relevant float, then nothing else needs to be done.  No clearance is
added.

Otherwise, recompute the hypothetical position, but this time do not
collapse the element's top margin with any margins above it.  Collapse
any other appropriate margins.  Then set the clearance equal to the
amount necessary to make the top border edge of the cleared element
flush with the bottom outer edge of the lowest relevant float.  (The
clearance amount may be negative, if the new hypothetical position
would place the top border edge of the element below the bottom outer
edge of the lowest relevant float.)
"""

As well, delete the explanatory paragraph immediately below the
example, and replace it with the following text:

"""
Explanation: Without the 'clear', the first and last paragraphs'
margins would collapse and the last paragraph's top border edge would
be flush with the top of the floating paragraph. But the 'clear'
requires the top border edge to be below the float, i.e., 2em lower.
Recomputing the position of the last paragraph without letting the
margins collapse then places the top border edge of the last paragraph
7em (4em + 3em) below the border edge of the first paragraph, or 1em
below the bottom outer edge of the float.  So, the clearance must be
set to -1em to bring the border edge of the last paragraph flush with
the bottom outer edge of the float.
"""

This should definitely be clearer, and I *believe* it describes the
exact same behavior as the current spec.

~TJ
Received on Thursday, 3 June 2010 23:52:06 GMT

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