What purpose do sizcache and sizset serve in jQuery-open source projects jlong/serve

I am using jQuery, and in inspecting the DOM of my page in IE with the Dev Toolbar I see that many elements have sizset and sizcache attributes added to the element. I don’t see these in Chrome or Firefox? Also, I see that many elements on the page share the same value for these fields leading me to believe it was a global value, but a few do have different values?

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Does anyone know why IE only shows these, and what purpose they serve?