mInnerScriptLevel = mPresentationData.scriptLevel + increment;
  SetInitialChildList(nsIPresContext* aPresContext,                      nsIAtom*        aListName,                      nsIFrame*       aChildList)  {    nsresult rv;    rv = nsMathMLContainerFrame::SetInitialChildList(aPresContext, aListName, aChildList);    // 1. The REC says:    //    The <mfrac> element sets displaystyle to "false", or if it was already    //    false increments scriptlevel by 1, within numerator and denominator.    // 2. The TeXbook (Ch 17. p.141) says the numerator inherits the compression    //    while the denominator is compressed    PRInt32 increment =       NS_MATHML_IS_DISPLAYSTYLE(mPresentationData.flags) ? 0 : 1;    UpdatePresentationDataFromChildAt(aPresContext, 0, -1, increment,      ~NS_MATHML_DISPLAYSTYLE,       NS_MATHML_DISPLAYSTYLE);    UpdatePresentationDataFromChildAt(aPresContext, 1,  1, 0,       NS_MATHML_COMPRESSED,       NS_MATHML_COMPRESSED);    // check whether or not this is an embellished operator    EmbellishOperator();    // even when embellished, we need to record that <mfrac> won't fire    // Stretch() on its embellished child    mEmbellishData.direction = NS_STRETCH_DIRECTION_UNSUPPORTED;    // break the embellished hierarchy to stop propagating the stretching    // process, but keep access to mEmbellishData.core for convenience    mEmbellishData.firstChild = nsnull;    return rv;  }