[R] R-lang.epub is invalid according to epubcheck

[Mstislav Elagin]

Hello R folks,

when validating the epub version of "The R language definition" from

https://cran.r-project.org/doc/manuals/r-release/R-lang.epub

with epubcheck (https://github.com/w3c/epubcheck), the latter reports 490
errors. According to the Makefile in R sources, epubs are being produced
using calibre. Using another converter
(https://github.com/jlhg/texinfo2epub ) that transforms via Docbook XSL
leads to a clean epub (according to the epubcheck). In the past I
encountered quite a few invalid epubs that confuse my e-ink reader and
were made by calibre. Might it be worth switching the epub converter?

Best regards
/me