The html link to 'Extending TFTP' near the bottom is broken. The href has a trailing period href="http://www.compuphase.com/tftp.htm." should be href="http://www.compuphase.com/tftp.htm"
This is neither a problem with tftp(1) nor mandoc(1); rather it seems to be a problem with the online man page browser. Running "mandoc -T html tftp.1 produces the correct output, like this: <cite class="Rs" title="Rs"><span class="RsT">Extending TFTP</span>, <a class="RsU" href="http://www.compuphase.com/tftp.htm">http://www.compuphase.com/tftp.htm</a>.</cite> However, the online man pages (https://www.freebsd.org/cgi/man.cgi?query=tftp&apropos=0&sektion=0&manpath=FreeBSD+12-current&arch=default&format=html) format it incorrectly, like this: <i>Extending</i> <i>TFTP</i>, <a href="http://www.compuphase.com/tftp.htm.">http://www.compuphase.com/tftp.htm.</a> I don't know if the online man browser is using an older version of mandoc, or something else entirely.
(In reply to Alan Somers from comment #1) The online manual pages are generated using man.cgi which as the name implies is an old perl script that was written by wosch@ back in 1999. As part of the website redesign, I hope to get the man-pages generated with mandoc -Thtml instead, as these are not only considerably quicker (as it can be run via make jobs on the server), but also generate HTML anchors for .Sh and .Ss macros.