taggedblock cannot be nested

[tperami]

If you do:

\begin{taggedblock}{tag1}
  \begin{taggedblock}{tag2}
  a
  \end{taggedblock}
\end{taggedblock}

Then enabling tag1 but not tag2 is enough to show a which is wrong.

[yloiseau]

moreover, enabling tag2 but not tag1 causes a error at the second \end{taggedblock}