code: def set_alpha(node, alpha=0.1):
      
      for child_node in node.findall(".//*[@rgba]"):
          rgba_orig = string_to_array(child_node.get("rgba"))
          child_node.set("rgba", array_to_string(list(rgba_orig[0:3]) + [alpha]))
docs: Sets all a(lpha) field of the rgba attribute to be @alpha
      for @node and all subnodes
      used for managing display