Quick Clojure: Understanding Dot Dot Macro

user> (. "hello " trim)
"hello"
user> (. (. "hello " trim) toUpperCase)
"HELLO"
user> (.. "hello " trim toUpperCase)
"HELLO"
user> (.. "hello " trim toUpperCase length)
5
user> (.. "hello " trim toUpperCase (concat " world"))
"HELLO world"