Feature: Allow users to set CSS classes on nodes similar to `setStyle`

This would make it compatible with tailwind. Since spans are used anyway it should just be a matter of setting a different property on the element.

Start by locating the node handling for setStyle and the span elements mentioned in the issue. Trace how styles are applied, then determine where a CSS class property would be exposed and rendered. Done means users can assign classes to nodes and Tailwind classes appear on the resulting elements.

Written by the indexing model from the issue text.