template<typename target, template<class> class use, class Option, typename tag, typename... tags>
tk::grm::action<back_back_store_option<target, use, Option, tag, tags...>> struct

Push back option to vector of back of vector in state at position given by tags.

This struct and its apply function are used as a functor-like wrapper for storing an option (an object deriving from tk::Toggle) in a place in the stack. tag and tags... address a vector of vectors, whose inner value_type is a nested tagged tuple whose field in where we store here after conversion, indexed by target. See walker::ctr::DiffEq for an example specialization of tk::Toggle to see how an option is created from tk::Toggle. We also do a simple sanity check here testing if the desired option value exist for the particular option type and error out if there is a problem. Errors and warnings are accumulated during parsing and diagnostics are given after the parsing is finished.