code: def union_to_html(union) -> ET.Element:
      div = ET.Element(
          "div", attrib={"class": "river-component river-union"}
      )
  
      for transformer in union.transformers.values():
          div.append(to_html(transformer))
  
      return div
  
file_path: river/river/base/viz.py
imports: from __future__ import annotations
  import inspect
  import textwrap
  from xml.etree import ElementTree
label_desc: Use image node_id 4 for calling a global function with example usage: union_to_html(union) and returns: div