Support for tagging (special) blocks

[Sébastien Miquel]

Hi,

I've been using tags on special blocks, src blocks and other, for two
purposes:

 1. to control which blocks get exported, using the `#+exclude_tags`
    property.
 2. to fine tune the export, according to tags, of special blocks such as
    #+BEGIN_exercice                                            :hard:
    …
    #+END_exercice

Does anyone think this is useful and might warrant adding support for ?

--
Sébastien Miquel