used to be "texdoc dvipdfmx", now "texdoc -l
dvipdfmx" option 2
I still get the user's manual as option 1, as far as I can see.
$ texdoc -l dvipdfmx
1 /usr/local/texlive/2017/texmf-dist/doc/dvipdfmx/dvipdfmx.pdf
2 /usr/local/texlive/2017/texmf-dist/doc/dvipdfmx/dvipdfmx-special.pdf
...