Action view templates can be written in various ways depending on the format of the response. If the response is in html format then we can use .erb files i.e. html files, with embedded ruby in it. If the format is in xml then we need to use files with .builder extension. Builder::XmlMarkup library is used for these templates.

In templates with .xml.builder extension we use a xml object . This is an object of XmlMarkup class. Example :

xml.a("Findnerd", "href" => "http://findnerd.com") 

# => <a href="http://findnerd.com">Findnerd</a>

In the above example .a is a method of the object xml. Any such method within a block of another method gives a nested xml output. Example:

def  index
@users = User.all
      respond_to do |format|
         format.xml {render :xml => @users}
      end
end

In the index.xml.builder file we can write like this to generate xml view:

xml.instruct!         
@users.each do |user|
     xml.div do
       xml.p(user.name)
       xml.p(user.email)
     end
end

Assuming there are only 2 user outputs of the above code, then it will be something like this:

<div>
  <p>David</p>
  <p>david@gmail.com</p>
</div>
<div>
  <p>Joe</p>
  <p>joe@hotmail.com</p>
</div>