Currently, to create an owning bson_value::value, users must first construct a bsoncxx::document::value, then parse out the bson_value they are interested in:

auto doc = make_document(kvp("v", "message"));
auto owning_value = doc.view()["v"].get_owning_value();

This is not an ideal workflow.  To avoid it, we will need to provide a way for users to construct bson_value::value directly.  We should not utilize the b_type structs for this, because those structs are inherently non-owning, and would require a copy for us to use them to implement these constructors.  Instead, we should consider exposing a series of bson_value::value constructors that take the component members for each b_type. 

For example, something like:

// constructor for b_document
value(document::view_or_value doc);

// constructor for b_oid
value(oid object_id);

// constructor for b_regex
value(std::string regex, std::string pattern);

// constructor for b_binary
value(binary_sub_type sub_type, uint32_t size, std::unique_ptr<uint8_t[]> bytes);

With such constructors the workflow would be simpler and more straightforward:

bson_value::value owning_value{"message"};