An additional complication is introduced by the fact that OB markers may shift depending on the political climate, so a topic that was previously permissible may be banned in the future, and "vice versa". In 1999, George Yeo said that it is difficult to define exactly what the OB markers are in advance. "Straits Times" editor-in-chief Cheong Yip Seng found OB markers "bewildering", stating that topics deemed off-limits during his tenure included stories about a stamp dealer, carpet auctions, monosodium glutamate, feng shui and unflattering pictures of politicians.