Rdo_set_sectag sets atrribute "Rd_tag" of the object s
to eltag, then wraps s in list() with "Rd_tag"
attribute sectag.
The remaining functions provide one-argument access for some
frequently used special cases. eltag is "TEXT" for
Rd_title and "VERB" for Rd_name and Rd_args. The
values of sectag are \title, \name and
\arguments, respectively.