If anyone has any ideas of this bug: https://bugs.webkit.org/show_bug.cgi?id=47745 I'd appreciate the help. Basically, when the MathML is wrapped in an anchor parent, the focus event causes a crash at: ASSERTION FAILED: !renderer()->needsLayout() (/Users/alex/workspace/WebKit/WebCore/dom/Node.cpp:793 virtual bool WebCore::Node::isFocusable() const) The node in question is the anchor itself. It is marked as needed layout, which I presume is coming from the MathML rendering objects, but all the children rendering objects are marked as not needing layout. If you try out the example attached to the bug, just click on the tiny "x" in the example. That will cause the crash. My guess is that this is related to a larger issue of layout not propagating correctly with MathML. In certain situations, I've seen MathML layout overflow containers and then a simple window resize or similar user action will cause everything, including the MathML, to reflow correctly. I haven't narrowed down specific cases of this problem quite yet. -- --Alex Milowski "The excellence of grammar as a guide is proportional to the paucity of the inflexions, i.e. to the degree of analysis effected by the language considered." Bertrand Russell in a footnote of Principles of Mathematics