See http://www.w3.org/TR/MathML/chapter3.html#id.3.2.5.7.3
fred@igalia-fwang:~/webkit/WebKit/Source/WebCore$ find . -type f -name '*.cpp' -o -name '*.h' | xargs grep 124831 ./rendering/mathml/RenderMathMLOperator.cpp: // FIXME: The spacing should be added to the whole embellished operator (https://webkit.org/b/124831).