def _set_default_configuration():
    """Return a default configuration based on fields defined on the
        schema.

        This should be a dictionary.  But, we have at least one
        exception: the css_class field simply has a string.  This
        might change in the future if this bites us.

        All fields with dictionaries must have, at least, the
        following attributes:

        visibility: (u'on', u'off')
            is the field visible? defaults to u'on'
            XXX: this could be a boolean in the future
        order: (u'1', u'2', ...)
            in which order we are going to display the field?
            XXX: until we fix the UI, we must start with 1 instead of 0
                 because is most intuitive for end users

        the following attribute is available only in TextLine fields:

        htmltag: (u'h1', u'h2', ...)
            defaults to u'h2'
            XXX: this name is a bad one, but I have no proposal for now

        the following attributes are available only in NamedImage fields:

        position: (u'inline', u'left', u'right')
            defaults to u'left'
            XXX: this should be named 'alignment' probably
        imgsize: (any of the available sizes for scaled down images)
            defaults to u'mini 200:200' or first available size
            XXX: this should be named 'scale' probably

        final result will be something like this:

        {'css_class': u'tile_default',
         'date': {'order': u'3', 'visibility': u'on', 'format': 'datetime'},
         'description': {'order': u'1', 'visibility': u'on'},
         'image': {'imgsize': u'mini 200:200',
                   'order': u'2',
                   'position': u'left',
                   'visibility': u'on'},
         'subjects': {'order': u'4', 'visibility': u'on'},
         'title': {'htmltag': u'h2', 'order': u'0', 'visibility': u'on'},
         'uuid': {'htmltag': u'h2', 'order': u'5', 'visibility': u'on'}}

        Obviously some of the fields are not meant to be displayed,
        like css_class, but that's another story.
        """
