Okay, created a defcustom for it. Patch is attached.

On Sun, Mar 22, 2015 at 7:03 AM, Stefan Monnier <monnier@iro.umontreal.ca>
wrote:

> > He could break the attribute onto a new line and it would be indented
> like
> > so:
>
> > <element
> >    attribute="value">
>
> > But sgml-basic-offset defaults to 2, not 3, so it doesn't make much sense
> > that
> > the attribute is indented by 3 spaces.
>
> As is clear from the code you're changing the "1+" is quite deliberate,
> which shows some people prefer it that way.
>
> So as discussed, this indentation step should have its own custom var.
> You can make it default to the behavior you prefer if you want.
>
> Other than that, the patch looks OK.
>
>
>         Stefan
>