# Default for mo@symmetric is wrong #469

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opened this issue May 17, 2013 · 6 comments

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### dpvc commented May 17, 2013

 The default for mo@symmetric should be false but is true in the mml ElementJax code. It should be changed to false.
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### fred-wang commented Jun 12, 2013

 OK, I guess it is easy to fix, but I'm not sure how to write a test that will detect the change (perhaps it's not necessary).

### dpvc pushed a commit to dpvc/MathJax that referenced this issue Feb 8, 2014

 Fixed default value for mo@symmetric. Resolves issue mathjax#469. 
 eb0cae8 

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### dpvc commented Feb 8, 2014

 A test case could compare a stretchy vertical arrow with symmetric="true" to one without symmetric to see if the results are the same or different (image comparison). Vertical arrows should default to symmetric="false".
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### dpvc commented Feb 9, 2014

 It turns out that the spec was inconsistent on this (listed the default as both false and true). I asked for clarification on the MathML mailing list, and they indicated it should be "true" (as currently implemented in MathJax). Here is part of the conversation (from David Carlisle): All the boolean attributes other than symmetric default to false, so in the operator dictionary interpreting the lack of the property name as the default or as false comes to the same thing. For symmetric, now it's clarified as defaulting to true, as written an operator dictionary could set it to false but the compressed notation used in appendix C can not express that and so in fact they are all true and "symmetric" in the table no effect other than a visual hint in the sample dictionary. An alternative would be to say that an omitted boolean property name means false, but then we would have to check whether it needs adding to more entries eg the vertical arrows which are the majority of vertically stretchy characters for which currently symmetric isn't explicit in the table. So I'm deleting the branch where I made the change, and closing this issue (marking it "expected behavior").

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### dpvc commented Feb 10, 2014

 Well, it turns out that the default really is supposed to be false after all: Neil later checked the archives and the decision to change the default to false and add entries making it true for brackets in the operator dictionary was deliberate before MathML3. This fits better with arrows and also with the presentation style used for boolean attributes in the appendix (although that could have been changed of course). so I'm reopening the issue, and will resurrect my path from above.

### dpvc pushed a commit to dpvc/MathJax that referenced this issue Feb 10, 2014

 Merge branch 'issue469' into develop. Issue mathjax#469. 
 e1b0093 

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### dpvc commented Feb 10, 2014

 => Merged

### dpvc pushed a commit to mathjax/MathJax-test that referenced this issue Apr 21, 2014

 Add test for issue mathjax/MathJax#469. 
 3b6caf3 
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### dpvc commented Apr 21, 2014

 => In Test Suite. MathMLToDisplay/Topics/StretchyChars/issue469.html