> rd2html("\\url{}")
Error: Failed to parse \url{}.
i Check for empty \url{} tags.

> rd2html("\\url{a\nb}")
Error: Failed to parse \url{}.
i This may be caused by a \url tag that spans a line break.

> rd2html("\\email{}")
Error in x[[1]]: subscript out of bounds

> rd2html("\\linkS4class{}")
Error: Failed to parse \linkS4class{}.

> rd2html("\\enc{}")
Warning in tools::parse_Rd(con, fragment = fragment, encoding = "UTF-8"): bad markup (extra space?) at <connection>:1:7

character(0)

