Do Volker's tabindex changes, but from and to the develop branch rather than master. :-)
I changed the default to inTabOrder: true, and refactored the code that sets all the tabIndex values so that they can be called by the page author to remove/set all the indices if they want. I removed the menu item action value, since selecting any menu item causes the tabindices to be reset, so no special action needs to be take for this menu item. I left the getTabOrder() function, since it includes logic that is needed to get the index from the menu setting, and using the function prevents that from being duplicated everywhere. As a side-effect, a page author could override it, but that is not its main purpose. I added a jax parameter to getTabIndex() so that, if overridden, it could be used to identify which math element was being processed.