gistfile1.rb

#Changing the default behavior of field Errors
# config/initializers/field_errors.rb

ActionView::Base.field_error_proc = Proc.new do |html_tag, instance|
  msg = instance.error_message
  if html_tag =~ /<(input|textarea|select)[^>]+class=/
    class_attribute = html_tag =~ /class=['"]/
    html_tag.insert(class_attribute + 7, "error")
  elsif html_tag =~ /<(input|textarea|select)/
    first_whitespace = html_tag =~ /\s/
    html_tag[first_whitespace] = " class='error' "
  end
  html_tag
end