1.nesting route(second level routes) -- to navigate to another route component inside of route component
a.to =/home/a/b path=/home/a/b (route path will match to value by the order of route declared)
b.also the reason why we shouldn't use exact match, sometimes nesting routes will be ignored
c.add swtich and redirect
2.pass value to nested route component(children component)
a.pass value in params
b.pass value in search
c.pass value in state
3.declarative routing
a.add push button
b.add replace button
c.goback/goforward/goto
d.navigate to messages tab(link) in 3 secs
4.withRouter
