template<template<class> class use, class Option, typename tag, typename... tags>
tk::grm::action<store_back_back_option<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 pushing back an option (an object deriving from tk::Toggle) into the back of a vector of a vector in the grammar stack. 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. This functor is similar to store_back_option but pushes the option back to a vector of a vector.