code: func (t Expander) Validate(template string) (pkg string, err error) {
  	return t.expandImpl(template, true)
  }
docs: // Validate returns an error if this template doesn't appear to be valid given
  // the current Expander parameters.
  //
  // This will catch issues like malformed template parameters and unknown
  // variables, and will replace all ${param=value} items with the first item in
  // the value list, even if the current TemplateExpander value doesn't match.
  //
  // This is mostly used for validating user input when the correct values of
  // Expander aren't known yet.