Dear,

As proposed in interface3.pdf, I hereby inform that in the next version 
of the wheelchart package, I plan to use some of the \tl_build_... 
functions from l3candidates. Namely

\tl_build_begin:N
\tl_build_end:N
\tl_build_gbegin:N
\tl_build_gend:N
\tl_build_gput_left:Ne
\tl_build_gput_right:Ne
\tl_build_put_right:Ne
\tl_build_put_right:Nn
\tl_build_put_right:NV

Kind regards,
Matthias Floré