It started with this Idea after fixing a bug I found with field_with_errors :
Instead of wrap an invalid input with
class (or data-attr.) to the input element itself.
Which is required by some frontend frameworks or if the project
requirements don’t allow extra markup around inputs with errors.
After a research, field_error_proc looked promising but required parsing and
manipulating the full rendered HTML element. , 
Of course, this works but just didn’t feel right.
I thought, Instead of parse & manipulate the full rendered HTML fragment after
just define a global error html_options that will be merged into the AV::FormHelper object before.
So I started coding…
I’m not super happy with the current test setup. I wanted to avoid a lot of c&p for setup and teardown.
So I’ve oriented myself on the asset_tag_helper_test.rb dry pattern. Feedback, of course, is welcome!
I’ve summarized my work in this PR:
p.s. I apologize for sending this email after creating the PR!