Hello,

$ cat test
require "cgi"
#cgi = CGI.new("html3")  # ==> no error
cgi = CGI.new("html4")
cgi.out do
  cgi.html do
    cgi.body do
      cgi.center do
        cgi.p do
          "text"
        end
      end
    end
  end
end
$ ruby test
test:7: undefined method `center' for #<CGI:0x402b8d64> (NoMethodError)

cgi.html{  # ==> parse error
cgi.br     # ==> <BR>
cgi.br{}   # ==> <BR>         # (BR element has no close tag) 
cgi.h1     # ==> <H1></H1>    # (H1 element can not omit close tag)
cgi.h1{}   # ==> <H1></H1>


-- 
Wakou Aoyama  <wakou / ruby-lang.org>