Markaby syntax question


I am just getting into Rails and I thought I'd try Markaby too.

I have a mab file with the following in it:

   form_for :user do |form|

      p do
        label "First Name:", :for => "first_name"
        form.text_field :first_name, :size => 40

(... cut similar)

     submit_tag "Add User", :class => "submit"


This renders the label but does not render the text field. If I
comment out the label line, it renders the text field. Why can't I get
both to work, what am I doing wrong?