en	= Avoiding Physical Dependency Some users, particularly library authors, may wish to provide conversions between their types and <<ref_value>>, but at the same time would prefer to avoid having their library depend on Boost.JSON. This is possible to achieve with the help of a few forward declarations.

en	Note that <<ref_value_from>> is declared using an out-parameter, rather then returning its result. This overload is specifically designed for this use-case.

en	After that the definitions of `tag_invoke` overloads should be provided. These overloads have to be templates, since <<ref_value>> is only forward-declared and hence is an incomplete type.

en	As discussed previously, we prefer to define a non-throwing overload of `tag_invoke` for <<ref_try_value_to>>, rather then the throwing overload for <<ref_value_to>>, as the latter can fallback to the former without performance degradation.

en	Forward declarations of contextual conversions are done very similarly: