谢谢，fdsa！

为了子孙后代，这里是我实际使用的代码。它将版权、注册、商标、服务商标和欧元添加到允许的实体阵列中。我很困惑，为什么其中一些默认情况下不存在，因为它们确实很常见。但无论如何，这是可行的：

// Custom configuration for TinyMCE
function wpsx_54398_configure_tiny_mce( $initArray ) {

    // Add some common entities to the default array (copy, reg, trade, service mark, euro)
    // The odd entires are the entity *number*, the even entries are the entity *name*. If the entity has no name,
    // use the number, prefixed with a hash (for example, the service mark is "8480,#8480").
    $initArray[\'entities\'] = $initArray[\'entities\'] . \',169,copy,174,reg,8482,trade,8480,#8480,8364,euro\';

    return $initArray;

}
add_filter(\'tiny_mce_before_init\', \'wpsx_54398_configure_tiny_mce\');