Use `tabindex="0"` instead of `href="#"` for controls?

Ideally <button> should be used for controls (https://github.com/Leaflet/Leaflet/issues/7821), however migrating from <a> to <button> is likely to break a lot of selectors in the wild. Instead, it may be better to use tabindex="0" for now (same as for markers), as it behaves more similarly to <button>:

1. tabindex="0" does not prompt a URL to be displayed when hovered/focused (more aesthetically pleasing, but also removes a potential source of confusion for some users):
   
   
   
2. tabindex="0" does not cause a “touch callout” on taphold:
   
   

[jonkoops]

Perfect, we can see if we can land that in another PR. I personally have no objections for adding a tabindex="0" here.

[Malvoz]

I personally think we should use the button element here, a link is semantically wrong as we aren’t actually linking anywhere. This would be a breaking change we can make in Leaflet 2.

@jonkoops note that most controls use the correct semantics due to role="button" (there are some controls that don’t, I’ve opened issues for those). Anyhow, I’ve opened https://github.com/Leaflet/Leaflet/issues/7821 for moving from <a> to <button>.