Updatexml function again in effect mysql

Explain the function

http://www.blogjava.net/chenpengyi/archive/2006/07/11/57578.html

My understanding is that updatexml function has a search function and you will again xpath query will be displayed at the grammatical structure of the error and then it will be the results of his inquiry has been given in the form of

Hey very comfortable learning day finally understand why the use of this function

Then give some of your mysql usual syntax

Even good resource

https://www.cnblogs.com/aqxss/p/6563625.html