simple
.
.. subfigure:: AB

   .. image:: image.png
      :alt: hallo

   .. image:: image.png
      :alt: hallo
.
<document source="<src>/index.rst">
    <figure classes="sphinx-subfigure" grid_classes="" is_subfigure="True" item_classes="" layout="['A',\ 'B']" subcaptions="True">
        <SubfigureGridHtml layout="['A',\ 'B']">
            <SubfigureGridItemHtml area="A" classes="sphinx-subfigure-item">
                <image alt="hallo" candidates="{'*': 'image.png'}" subfigure_area="A" uri="image.png">
            <SubfigureGridItemHtml area="B" classes="sphinx-subfigure-item">
                <image alt="hallo" candidates="{'*': 'image.png'}" subfigure_area="B" uri="image.png">
.
