The following example fails to compile, complaining “Missing { inserted.”

It compiles cleanly if one or more of the three marked lines are removed.

This is the case with TL2013 and with recent standalone beta versions. I do not know if it ever worked.

\setuplayout   [grid=yes]%                            line one
\definetextbackground[TB][
                 topoffset=.25em,bottomoffset=.25em,% line two
                 location=paragraph,%                 line three
                ]
\starttext
\startTB
prisca iuvent alios ego me nunc denique natum gratulor: haec
aetas moribus apta meis.
\stopTB
\stoptext

--
Rik