Hi,

If you use the command \DeclareDocumentCommand and the command name 
already exists, you will get the warning "LaTeX warning 
"xparse/redefine-command" " initialized by

\msg_kernel_warning:nnxx { xparse } { redefine-command }


I think most package authors will use this command. (e.g. fontspec)

Based on this fact you will get a lot of warnings. In my opinion 
warnings become ineffectually.

So I suggest to use \msg_kernel_info:nnxx { xparse } { redefine-command }

What do you think?


xparse.sty l. 105-119
xparse.dtx l. 873-887


\cs_new_protected:Npn \xparse_declare_cmd_aux:Nnn #1#2
   {
     \cs_if_exist:NTF #1
       {
         \msg_kernel_info:nnxx { xparse } { redefine-command }
           { \token_to_str:N #1 } { \tl_to_str:n {#2} }
       }
       {
         \msg_kernel_info:nnxx { xparse } { define-command }
           { \token_to_str:N #1 } { \tl_to_str:n {#2} }
       }
     \prop_put:Nnn \l_xparse_command_arg_specs_prop {#1} {#2}
     \bool_set_false:N \l_xparse_environment_bool
     \xparse_declare_cmd_internal:Nnn #1 {#2}
   }


best regards
Marco