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[csswg-drafts] [css-values-4] Difference of viewport and initial containing block size (#5218)

From: zjopy via GitHub <sysbot+gh@w3.org>
Date: Tue, 16 Jun 2020 15:30:20 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-639767283-1592321418-sysbot+gh@w3.org>
zjopy has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-values-4] Difference of viewport and initial containing block size ==
What is the difference between the size of the viewport and the size of the initial containing block (ICB)? The current spec is contradicting itself. There are two possibilities

1. Size is the same

as defined by 10.1 in [CSS2](https://www.w3.org/TR/CSS22/visudet.html#containing-block-details)

> For continuous media, [the ICB] has the dimensions of the viewport [..].

2. Size of viewport is visible part of document (without scrollable area due to overflow), size of ICB is whole document (with scrollable area due to overflow).

as defined by the note in [css-values-4](https://www.w3.org/TR/css-values-4/#viewport-percentage-lengths)

> Note that the initial containing block’s size is affected by the presence of scrollbars on the viewport.

Whatever the answer might be, there is a bug in [css-values-4](https://www.w3.org/TR/css-values-4/#viewport-percentage-lengths). If the answer is 1., then the note quoted in 2 is erroneous. If the answer is 2., then the definition of the viewport-percentage lengths is erroneous.

> The viewport-percentage lengths are relative to the size of the initial containing block.

Yes, the spec excludes the scrollable area afterwards 

> However, when the value of overflow on the root element is auto, any scroll bars are assumed not to exist.

But then, this is exactly the difference between the size of the viewport and the ICB. So the spec should just use the correct term. Defining an exception for a term (ICB) that is used to differentiate from another term (viewport) but making the exception so the term equals the other term from which it tried to differentiate itself in the first place is ... confusing, to say the least.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/5218 using your GitHub account
Received on Tuesday, 16 June 2020 15:30:22 UTC

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