Allow the attribute used to find error elements to be specified

[madmatt]

To properly use the errorElement setting, you generally also need to change the attribute that validation uses to determine whether an error message exists already. By default, the plugin uses the label element, and the for attribute. For example: <label for="form_field_id">Your error message here</label>

Changing the errorElement to span for example fixes one accessibility issue (that you can't have more than one label element per input due to screen reader issues), but brings up another one - <span for="form_field_id">Error message here</span> is not valid HTML, as a span element can't have the for attribute.

Therefore, we need a way of also specifying which attribute of the element to check, instead of hard-coding the for attribute. Then, we could use data-for in cases where the for attribute isn't legal.

[madmatt]

At a brief glance, this should be relatively easy to fix (two one-line code changes and a new addition to this.settings), I'll try and get a PR through for this if it makes sense to others as well as me!

[nschonni]

I did #900, but I haven't gone back to fix and merge it yet

[jzaefferer]

I'm sorry for the lack of activity on this issue. Instead of leaving it open any longer, I decided to close old issues without trying to address them, to longer give the false impression that it will get addressed eventually, especially after several years with no activity. It doesn't mean I'm abandoning the project, just that I'm unable to work through 200+ open issues with the little time I can afford to spend on this project.

To the reporter (or anyone else interested in this issue): If you're still affected by the same issue, please consider opening a new issue, with a testpage that demonstrates the issue with a current version of the plugin. Even better, make an attempt to fix the issue yourself, and improve the project by sending a pull request. This may seem daunting at first, but you'll likely learn some useful skills that you can apply elsewhere as well. And you can help keep this project alive. We've documented how to do these things, too. A patch is worth a thousand issues!