ruby-on-rails-3 - Rails 3 - Calendar Date Select Gem - Disable Field Input

Question

Using gem 'calendar_date_select', :git => 'git://github.com/paneq/calendar_date_select.git' in my Gemfile.

Is there an option for disabling the user from keying in the date, forcing them to use the popup calendar? For some reason, if they key in the date by hand, the wrong date is stored.

Here it is on my form:

<%= f.calendar_date_select "invoice_date", :index => '1', :time => false, :size => 12 %>

Thanks in advance!