If a zero lengthed render object (such as a text node that has been set to "") occured at the end of a line, it was previously given a non-zero sized run.
A crash would occur on iteration over a node containing such a run. NodeIterators, the innerText property, and hovering over a link all use iteration.
This tests iteration using both the innerText property and NodeIterators. It is successful if it doesn't crash Safari.