Make controls button elements since they are buttons. Buttons are for actions, links are to take you to another page.

[prushforth]

This was the suggestion of @Powersurge on a11yslackers. He is correct, and perhaps this issue should be raised over at the Leaflet.js project, since the zoom control comes from there.

[Malvoz]

To my understanding, anchors are perfectly valid as buttons in this instance because role="button" is used, the buttons have accessible labels, and they respond correctly to keyboard input. Although I'm not certain, I think the usage of <a> is because buttons and other form elements are generally harder to style, e.g. they don't inherit font styles by default, and CSS appearance doesn't have (or didn't have at the time) wide enough browser support to warrant its use.

Anyhow, there's a leaflet issue to tackle some accessibility issues in Leaflet/Leaflet#3210, including moving from links to buttons.

[prushforth]

I think that's good enough for me at this time. Closing; feel free to discuss if necessary.

[Malvoz]

#19 (comment):

they respond correctly to keyboard input

That statement is incorrect, filed upstream issue: Leaflet/Leaflet#7369.

[Malvoz]

This issue should consider not only Zoom controls but all standard Leaflet controls, such as a popup's Close button, Fullscreen control, Layer control.