Insert text in the middle of text file by sed

I found problem on how to add text line in the middle of the hosts file. Just like below


127.0.0.1   localhost
< i want to add text line here >
xxxxxxxxxxxxxxx
xxxxxxxxxxxxxxx


and want to use 'sed', My friend, Sajal Kayan (God of Scripting) introduce me on ref#1, actually I quite not understand that. So he get me 2 approaches.


#1
  for each time i have to add text line, then do
  >>> sed -i 's/127.0.0.1   localhost/127.0.0.1   localhost\n this is new line /' /etc/hosts
  >>> sed -i 's/127.0.0.1   localhost/127.0.0.1   localhost\n this is new line 1/' /etc/hosts
  >>> sed -i 's/127.0.0.1   localhost/127.0.0.1   localhost\n this is new line 2/' /etc/hosts


  then we'll get


  127.0.01   localhost
  this is new line 2
  this is new line 1
  this is new line


  this is good enough if we don't care about the order. But if you care , Sajal has 2nd approach


#2
  >>> sed -i 's/127.0.0.1   localhost/127.0.0.1   localhost\n#dummyanchor/' /etc/hosts
  >>> sed -i 's/#dummyanchor/this is line 1\n/#dummyanchor/' /etc/hosts
  >>> sed -i 's/#dummyanchor/this is line 2\n/#dummyanchor/' /etc/hosts
  
  note that #dummyanchor is a comment , does not affect our system.


ref#1 http://www-rohan.sdsu.edu/doc/sed.html
ref#2 http://www.linuxquestions.org/questions/linux-general-1/bash-programming-append-single-line-to-end-of-file-265534/