求解释这个正则表达式的意思?(/^(\d{2})\d{4}(((\d{2})(\d{2})(\d{2})(\d{3}))|((\d{4})(\d{2})(\d{2})(\d{3}[x\d])))$/i)

求解释这个正则表达式的意思?
(/^(\d{2})\d{4}(((\d{2})(\d{2})(\d{2})(\d{3}))|((\d{4})(\d{2})(\d{2})(\d{3}[x\d])))$/i)

一串数字以数字或x结束.
像下面这样的(空格不算):
11 1111 11 11 11 111x
11 1111 11 11 11 1112
11 1111 1111 11 11 111x
11 1111 1111 11 11 1112