Réponses:
dwsupprime un mot et ce qui constitue un mot est défini par le iskeywordparamètre. De :h word:
word
A word consists of a sequence of letters, digits and underscores, or a
sequence of other non-blank characters, separated with white space (spaces,
tabs, <EOL>). This can be changed with the 'iskeyword' option. An empty line
is also considered to be a word.
Pour retirer _de iskeyword, faire:
set iskeyword-=_
*/ a #disparu.