build method
Implementation
@override
InlineSpan build() {
  return WidgetSpan(
    child: Padding(
      padding: EdgeInsets.only(top: parent == null ? 0 : config.marginBottom),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: List.generate(
          children.length,
          (index) {
            final childNode = children[index];
            return ProxyRichText(childNode.build(),
                richTextBuilder: visitor.richTextBuilder);
          },
        ),
      ),
    ),
  );
}