code: @Nullable
    private static RawTextNode getAttributeValue(
        HtmlTagNode tagNode, String name, ErrorReporter errorReporter) {
      HtmlAttributeNode attribute = tagNode.getDirectAttributeNamed(name);
      if (attribute == null) {
        return null;
      }
      RawTextNode value = getAttributeValue(attribute, name, errorReporter);
      // Remove it, we don't actually want to render it
      tagNode.removeChild(attribute);
      return value;
    }
docs: Returns the {@code RawTextNode} of the given attribute and removes it from the tag if it
  exists, otherwise returns {@code null}.
  
  @param tagNode The owning tag
  @param name The attribute name
  @param errorReporter The error reporter