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voice-volume, absolute and relative volume units [css3-speech][css3-values][CSS-ISSUE-184]

From: L. David Baron <dbaron@dbaron.org>
Date: Wed, 29 Jun 2011 15:43:23 -0700
To: www-style@w3.org
Message-ID: <20110629224323.GA13535@pickering.dbaron.org>
http://dev.w3.org/csswg/css3-speech/#voice-volume defines a relative
'dB' unit (which does make sense as a relative unit), which
CSS-ISSUE-184 proposes to move to css3-values.

However, the 'voice-volume' property then says its computed value is
"specified value", which doesn't make sense for relative values.  In
particular, an element with 'voice-volume: +5dB' should have a
different computed value depending on what its inherited value was.

We've had lots of problems in the past when we had properties whose
computed values couldn't be represented as valid syntax for the
property.  I think adding another such case (I think we've fixed the
existing ones, e.g., with the 'font-weight' changes in CSS 2.1) is a
bad idea.  So I think if you want relative units in this manner, you
should also have a syntax for combining them with the possible
absolute values.

Furthermore, the definition of <decibel> values for 'voice-volume'
says:
  # This represents a change (positive or negative) relative to the
  # default or inherited volume level.
which seems unnecessarily vague.  It should specify that it is
relative to the default for the root element and the inherited level
otherwise.

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/
Received on Wednesday, 29 June 2011 22:43:46 GMT

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