# Error when using ] in item title with math mode [duplicate]

I am getting the error

! Extra }, or forgotten $. \sbox ...hbox {\color@setgroup #2\color@endgroup } l.6 \item[$]
$] ! LaTeX Error: Something's wrong--perhaps a missing \item. With the MWB \documentclass{article} \begin{document} \begin{description} \item[$]$] \end{description} \end{document} It also fails when using $$]$$. Clearly that contained bracket is being matched as the one that closes the optional argument, so how do I prevent that? • Just write \item[${]}$]. – user121799 Nov 28 '17 at 20:13 ## 1 Answer A ] inside an optional argument with [] must be grouped into a {} pair (unless the macro is defined with \NewDocumentCommand etc. from xparse, which is not the case here) In my point of view there is no need for$]$then at all. \documentclass{article} \begin{document} \begin{description} \item[{]}] \end{description} \end{document} • "In my point of view there is no need for$]\$ then at all. " Well the non-minimal case I encountered is actually a math formula that contains ], so for my purposes, math mode is needed. But the general concept still works, so thanks. (I always figured math mode provided an implicit grouping, but I guess not.) [ by itself seems to work just fine either way, though.
– JAB
Nov 28 '17 at 20:17
• @JAB: You're right that [ works, but more rather by 'chance' . Grouping does no harm there.
– user31729
Nov 28 '17 at 20:20