Hi, There was already several questions about "user_defined" whatsits and I know that sometimes it can still influence the output (like there will be no font kern between two letters if there is a whatsit). I'm analyzing all available methods for marking output contents for tagged pdf or xml conversions. Now I noticed that it disables \last.. elements (like \lastskip, \lastpenalty) in vertical mode. In horizontal mode it doesn't influence \lastskip. So is it a bug? And could it be fixed in the future or this behavior will stay for ever? minimal example %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \directlua{ USER_MARK = node.new("whatsit","user_defined") USER_MARK.type = 115 USER_MARK.value = "my node" function writemark() local usermark = node.copy(USER_MARK) node.write(usermark) end } \def\addwhatsit{\directlua{writemark()}} \documentclass{article} \begin{document} \null \vskip 20pt \par \showthe\lastskip %% shows 20.0pt \null \vskip 30pt \par \addwhatsit \showthe\lastskip %% shows 0.0pt \null \hskip 10pt \addwhatsit \showthe\lastskip %% shows 10.0pt \end{document}