Few questions about web api versioning in core

just read a article on web api core versioning from this url http://www.c-sharpcorner.com/article/asp-net-core-api-versioning-in-simple-words-update-1-2-0/

i have few question about

[ApiVersion("2.0")]  and MapToApiVersion("2.0")

1) why we need to use two attribute for a controller and action called

[ApiVersion("2.0")]  and MapToApiVersion("2.0").

if i use

[ApiVersion("2.0")]

for controller then it should work for whole controller then why i need to decorate action with

MapToApiVersion("2.0")

2) why

[ApiVersion("1.0")]  and [Route("api/v{version:apiVersion}/[controller]")]

needed to decorate controller for versioning ?

3) this attribute

MapToApiVersion("2.0")

is used for action only and this [ApiVersion("1.0")] used for controller only ?


4)

[ApiVersion("2.0")] or MapToApiVersion("2.0")

for versioning then how web api action url would look like ?


please guide me.