Add class to body tag using diazo with notheme - plone

Question

i'm displaying the content of a document in an overlay using
plone/document?ajax_load=True&ajax_include_head=True as the src for an iframe.
in development mode appending &diazo.off=1 did the trick.
on the production server this sadly does not work, so i added the
ajax_load parameter as suggested in the documentation of plone.app.theming
i wrapped all my directives in a <rules if-not="$ajax_load"> element to make sure they are not applied (see code below)
now i'd need to mark the body of the iframed page with a certain class to apply different styles (eg no background color for the body in overlays)
the solution proposed for a nearly similar question does only work if you are using a theme with a body element having a class attribute to operate on.
is there a way to add a class to the content without having a theme (using )?
or do i have to supply an empty html document (index2.html) as theme and apply lots of rules to copy over css/js etc twice?
<rules if="$ajax_load">
<!-- theme href="index.html" /-->
<notheme />
<!-- only works when using a theme -->
<before theme-children="/html/body"><xsl:attribute name="class"><xsl:value-of select="/html/body/#class"/> my class</xsl:attribute></before>
<!-- thought this could to the trick but does not work at all -->
<xsl:template match="html/body">
<xsl:attribute name="class"> foo</xsl:attribute>
</xsl:template>
</rules>
<rules if-not="$ajax_load">
<theme href="index.html" />
<replace content="/html/head/title" theme="/html/head/title" />
...

Answer 1

Obviously without a theme to operate on, any rule referencing a theme does not work in conjunction with <notheme/>. You can however <drop> and <replace> content (I have ideas of how to implement <before> and <after> content, but its difficult to implement. Maybe in a future version of Diazo.) However you can achieve the same thing with a small amount of xslt:
<replace content="/html/body/#class">
<xsl:attribute name="class"><xsl:value-of select="."/> newclass</xsl:attribute>
</replace>

Answer 2

If you are using plone.app.jquerytools for your overlays, then you can pass a class parameter:
$('a.myPopover').prepOverlay({
subtype: 'iframe',
cssclass: 'my-popover'
});
In some of our project using plone.app.tiles we used a specific theme template for the overlays, that was stripped of all unecessary parts and reduced to a single wrapper div and used it for the tile edit view like so:
<theme href="minimal.html" if-path="##edit-tile" />