code: func (l *State) AbsIndex(index int) int {
  	if index > 0 || isPseudoIndex(index) {
  		return index
  	}
  	return l.top - l.callInfo.function + index
  }
docs: // AbsIndex converts the acceptable index index to an absolute index (that
  // is, one that does not depend on the stack top).
  //
  // http://www.lua.org/manual/5.2/manual.html#lua_absindex