In[206]:= Options[
Plot[x, {x, 0, 1}, PlotTheme -> "Web",
FrameLabel -> Automatic], FrameLabel]
Out[206]= {FrameLabel -> {{\!\(\*
TagBox[
InterpretationBox[
StyleBox[
GraphicsBox[{},
BaselinePosition->Baseline,
ImageSize->{0, 0}],
CacheGraphics->False],
Spacer[0]],
HoldForm]\), None}, {\!\(\*
TagBox["x",
HoldForm]\), None}}}