Decide how to handle begin/end pairs

[Infernio]

Right now the mockup uses

\begin_work_summary
This is the \em[summary] of the \st[entire work].
\end_work_summary

Nevermind the \em and \st, which is not how that works anymore since #2.

I think a better idea would be to have \begin and \end as generic commands, which take a 'context' argument:

\begin[work_summary]
This is the *summary* of the **entire work**.
\end[work_summary]

Have to think about where that would be defined and what such 'contexts' should even be able to do.