code: func substitute(ctx context.Context, templateString string, substitutions interface{}) (string, error) {
  	template, err := template.New(templateString).Parse(templateString)
  	if err != nil {
  		return "", err
  	}
  	buffer := bytes.Buffer{}
  	if err = template.Execute(&buffer, substitutions); err != nil {
  		return "", nil
  	}
  	return buffer.String(), nil
  }
docs: // substitute reads a template string and performs substitutions.
  //
  // Returns a string.