In a text, I get an overfull hbox
. To avoid this, I define an optional hyphenation point:
bla bla bla un\-known bla bla bla
pdflatex
indeed hyphenates the word at that point.
But when I declare the optional hyphenation point in the preamble like this
\hyphenation{un-known}
then pdflatex
will NOT hyphenate there.
The reason seems to be that LaTeX still thinks that the typeset text does not look good enough with the line break after 'un-'.
But then why is the behavior different for the inline optional hyphenation to the optional hyphenation declared in the preamble?
lua-visual-debug
and you'll see the possible hyphenation points.