observe_field and :on

ok, i found out that there is no :on parameter for observe_field
i noticed that it's not in documentation but found some examples where
people use it. i suppose they have some patched or older version of
rails where this was supported.

so, seems it's not possible to use "onkeydown" property of text field
with observe_field without patches.

installed autocomplete plugin instead

thanks for help everybody!)