Bug 16049 - Margin collapsing: clarification needed to Note in 10.7 (min-height and max-height)
Margin collapsing: clarification needed to Note in 10.7 (min-height and max-h...
Status: ASSIGNED
Product: CSS
Classification: Unclassified
Component: CSS Level 2
unspecified
All All
: P2 normal
: ---
Assigned To: Bert Bos
public-css-bugzilla
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Reported: 2012-02-20 21:41 UTC by Anton P
Modified: 2012-05-21 16:22 UTC (History)
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Description Anton P 2012-02-20 21:41:30 UTC
Reported by Anton Prowse.

At the F2F in Paris 2012
[http://lists.w3.org/Archives/Public/www-style/2012Feb/0529.html] there was a discussion about the note in 10.7 (min-height and max-height) which appears immediately after the algorithm describing the calculation of a tentative height and then used height (based on min-height and max-height).  The Note says:

  # These steps do not affect the real computed values of the above
  # properties. The change of used 'height' has no effect on margin
  # collapsing except as specifically required by rules for 'min-height'
  # or 'max-height' in "Collapsing margins" (8.3.1).

There was strong agreement that the second sentence is intended to mean that you determine whether and which margins collapse during the calculation of the tentative height, and that information remains fixed during any recalculation of the used height based on the values of min-height and max-height.  That is, you don't recompute anything with respect to margin collapsing.

I feel that this is not clearly captured by the Note.

Additionally, the mention of 'max-height' is confusing since there are no longer any rules concerning 'max-height' in 8.3.1 (since the spec changed a while ago, removing any special consideration of 'max-height').
Comment 1 Anton P 2012-02-20 21:41:44 UTC
Proposal

Replace:

  # These steps do not affect the real computed values of the above
  # properties. The change of used 'height' has no effect on margin
  # collapsing except as specifically required by rules for
  # 'min-height' or 'max-height' in "Collapsing margins" (8.3.1).

with:

  | These steps do not affect the real computed values of the above
  | properties. The change of used 'height' has no effect on margin
  | collapsing; the real computed value of 'height' is used to
  | determine which margins are adjoining in "Collapsing margins"
  | (8.3.1) during these steps.
Comment 2 Anton P 2012-04-11 15:54:30 UTC
An updated proposal is: [http://lists.w3.org/Archives/Public/www-style/2012Mar/0052.html]

Replace:
   # These steps do not affect the real computed values of the above
   # properties. The change of used 'height' has no effect on margin
   # collapsing except as specifically required by rules for
   # 'min-height' or 'max-height' in "Collapsing margins" (8.3.1).

with:

   | These steps do not affect the real computed value of 'height'.
Comment 3 Anton P 2012-04-11 16:01:30 UTC
The WG expressed an interest in keeping some sort of note about margin collapsing.  A possible second sentence could be:

# Consequently, for example, they do not affect margin collapsing, which depends on the computed value.
Comment 4 Anton P 2012-05-21 16:22:11 UTC
The WG resolved to accept the following change to close this issue.

Replace:
  # These steps do not affect the real computed values of the above
  # properties. The change of used 'height' has no effect on margin
  # collapsing except as specifically required by rules for
  # 'min-height' or 'max-height' in "Collapsing margins" (8.3.1).

with:
  | These steps do not affect the real computed value of 'height'.
  | Consequently, for example, they do not affect margin collapsing,
  | which depends on the computed value.


Minutes of resolution:
http://lists.w3.org/Archives/Public/www-style/2012Apr/0276.html
http://lists.w3.org/Archives/Public/www-style/2012Apr/0101.html