defaultAddFontsFromNode

The built-in rich-text font visitor: work out which face a node needs, register it, and pass the resulting state to the node's children.

Bold and italic marks switch weight and style; a code mark switches the whole family to the monospace one, because that is what the mark means. An app that adds a mark of its own wraps this — handle the mark, then delegate — rather than reimplementing the standard cases.