code: func isSearchWordRune(r rune) bool {
  	switch r {
  	case ':', ')', '(', eof:
  		return false
  	}
  	return !unicode.IsSpace(r)
  }
docs: // IsSearchWordRune defines the runes that can be used in unquoted predicate arguments
  // or unquoted literals. These are all non-space unicode characters except ':' which is
  // used for predicate marking,  and '(', ')', which are used for predicate grouping.