On 21/02/2012 12:02, dongen wrote: > \tl_new:N \l_arg_tl > \regex_const:Nn \c_slash_regex_tl { / } > \tl_set:Nn \l_arg_tl {1234/5678/9012} > \regex_replace_all:NnN \c_slash_regex_tl {\c{textbackslash}} \l_arg_tl > \regex_use:N \l_arg_tl ^^^^^^^^^^^ You want \tl_use:N -- Joseph Wright