\setupinteraction[state=start]

\definelayer[foo][width=300pt,height=300pt]
\setlayerframed[foo][width=300pt,height=300pt]{foo}


\starttext

\startbuffer[test]
\framed[offset=overlay]{\tooltip{\CONTEXT}{a \TEX\ macropackage}}
\stopbuffer

\setlayerframed[foo][x=0pt,y=0pt][offset=overlay]{\getbuffer[test]} % big skip in front of text
\flushlayer[foo]

\stoptext