Created attachment 81183 [details]
This was initially discussed on the MathJax user mailing list:
widevec, widehat and widetilde have stretchy set to "false" and thus do not stretch. It seems that setting stretchy="true" is not enough to make that work in other MathML rendering engines (at least not in Firefox for widetilde). As indicated in the MathML spec (http://www.w3.org/TR/MathML3/chapter7.html#chars.comb-chars):
"In the UCS there are many combining characters that are intended to be used for the many accents of numerous different natural languages. Some of them may seem to provide markup needed for mathematical accents. They should not be used in mathematical markup. Superscript, subscript, underscript, and overscript constructions as just discussed above should be used for this purpose. Of course, combining characters may be used in multi-character identifiers as they are needed, or in text contexts."
Hence I've also replaced the combining characters for tilde/hat by their non-combining versions and that fixes the stretchy issue. For vec it seems that "U+2192 RIGHTWARDS ARROW" (MS_RIGHTARROW) is what should be used and it renders better in Firefox. But the rendering is not very good in LibreOffice (font issue?) so I've kept the "U+20D7 COMBINING RIGHT ARROW ABOVE" for now.
LibreOffice still accepts the combining accents (or otherwise some unit tests fail).
Created attachment 81184 [details]
You can try to open this testcase in Firefox to see the difference.
Nice nice :-).
Lets mark it as NEW!
Kind regards and good job,
Marking these bugs assigned since I've already taken them.
Frederic Wang committed a patch related to this issue.
It has been pushed to "master":
fdo#66024 - Formula Editor: make wide accents stretchy when exported to MathML
The patch should be included in the daily builds available at
http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.