Hello,

I think, that would be easiest to add a new filed to the Page (menu item) document file, which will represent html5 attributes for that menu item and you will generate a menu through a transformation, in which you can render html5 attributes from your new field.

If you don't want to change the way you render the menu and you want to only add those attributes somehow into a menu item, you can use mentioned Menu item style field in the Menu section under the Properties tab and you can "hack" this field with the html5 attributes (by closing this attribute and opening your one):

" data-icon="search

Best regards,
Jan Hermann