delegate the rendering of the smippet placeholder to the snippet - that ...

...way I can over-ride it later

see https://github.com/SvenDowideit/mercury/issues/2

I'm not sure that this fits with your plans for snippets, but by delegating to the snippet class, i only need to over-ride that, rather than also patching the region 

(I want my html to contain the preview result, and the data- attributes to tell how we got to those results, possibly to be refreshed in future)

Sven