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[mediaqueries][css-values] Empty string value <media-query> or not

From: Simon Pieters <simonp@opera.com>
Date: Tue, 30 Sep 2014 12:05:54 +0200
To: www-style@w3.org
Message-ID: <op.xmzvn4obidj3kv@simons-mbp>
What is the correct interpretation of this grammar:

a? | b

If a is omitted, it does not occur (or occurs zero times), but | requires  
one of them to occur, so my understanding is that the above is equivalent  

a | b


Either way, it's confusing. Please make it clearer.

This is relevant for  

In particular, consider this media query list: ","

If the empty string matches <media-query> production then there are two  
empty <media-query>s (it's not defined if it matches or not AFAICT).

If the empty string does not match <media-query> production then it's  
equivalent to "not all,not all" per the error recovery rules (this matches  


If the interoperable browser behavior is intended, please remove the  
question mark.

Simon Pieters
Opera Software
Received on Tuesday, 30 September 2014 10:12:01 UTC

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