ge files over to a subdirectory of the output
directory on building (e.g. the ``_static`` directory for HTML output.)

Interpretation of image size options (``width`` and ``height``) is as follows:
if the size has no unit or the unit is pixels, the given size will only be
respected for output channels that support pixels (i.e. not in LaTeX output).
Other units (like ``pt`` for points) will be used for HTML and LaTeX output.

Sphinx extends the standard docutils behavior by allowing an asterisk for the
exten