src/serializers.js
function SpanSerializer(props) {
    const {mark, children} = props.node
    const isPlain = typeof mark === 'string'
    const markType = isPlain ? mark : mark._type
    const serializer = props.serializers.marks[markType]
    if (!serializer) {
      // @todo Revert back to throwing errors?
      // eslint-disable-next-line no-console
      console.warn(
        `Unknown mark type "${markType}", please specify a serializer for it in the \`serializers.marks\` prop`
      )
      return h(props.serializers.markFallback, null, children)
    }

    return h(serializer, props.node, children)
  }
function SpanSerializer(props) {
    const {mark, children} = props.node
    const isPlain = typeof mark === 'string'
    const markType = isPlain ? mark : mark._type
    const serializer = props.serializers.marks[markType]
    if (!serializer) {
      // @todo Revert back to throwing errors?
      // eslint-disable-next-line no-console
      console.warn(
        `Unknown mark type "${markType}", please specify a serializer for it in the \`serializers.marks\` prop`
      )
      return h(props.serializers.markFallback, null, children)
    }

    return h(serializer, props.node, children)
  }
Low-level span serializer