Return validation error to publish form from extension

Question

I've written an extension to do some additional processing on submitted form content within the ExpressionEngine publish page, however there is a scenario where I want to return an error to the user if a value they have specified is invalid.

Is there a way to do this with an extension, some function I can call to return a validation error but retain the form input so the user isn't forced to start again?

Obviously I could just use 'show_error' but this seems a little brutal and not what would be expected. :)

Answer 1

Check out this array:

ee()->form_validation->_error_array

You can check its contents and add to it. I forget the best hook to use this in, but it might be entry_submission_start?