I'd like an option to be able to specify that iOS and Android should not use auto-complete or auto-correct on certain text fields. I have two reasons.
  1. If you want text that's not natural language (e.g. a serial number, an ID) then if the mobile device does anything at all to change what the field user is typing, then it can only be unhelpful.
  2. For a long time, some of my users have been complaining about some special validation I had applied to a certain field, some saying it was unusable. But I was never able to reproduce the problem. Recently, I finally twigged that their device might be adding a trailing space to their input, invalidating it. Once I realised this, I updated my data event to strip trailing spaces and full stops (which iOS sometimes adds). So yes, you can work around this when you know, but the problem probably cost me a lot of trust and my users a lot of frustration. It's hard to anticipate this kind of thing when the web app doesn't behave in the same way.
I don't know if you can tell iOS and/or Android not to be "helpful", but if you can, I'd love to be able to.