您要么需要通过HTML编辑器添加此类代码（而不是切换回可视化编辑器），要么需要将自定义配置传递给可视化编辑器。

我也有类似的需求，下面是我在functions.php):

// http://tinymce.moxiecode.com/wiki.php/Configuration
function cbnet_tinymce_config( $init ) {

// Change code cleanup/content filtering config

    // Don\'t remove line breaks
    $init[\'remove_linebreaks\'] = false; 
    // Convert newline characters to BR tags
    //$init[\'convert_newlines_to_brs\'] = true; 
    // Preserve tab/space whitespace
    $init[\'preformatted\'] = true; 
    // Add to list of formats to remove with Remove Format button
    $init[\'removeformat_selector\'] = \'b,strong,em,i,span,ins,del,h1,h2,h3,h4,h5,h6,pre\';
    // Do not remove redundant BR tags
    $init[\'remove_redundant_brs\'] = false;

// Add to list of valid HTML elements (so they don\'t get stripped)

    // IFRAME
    $valid_iframe = \'iframe[id|class|title|style|align|frameborder|height|longdesc|marginheight|marginwidth|name|scrolling|src|width]\';
    // PRE
    $valid_pre = \'pre[id|name|class|style]\';
    // DIV
    $valid_div = \'div[align<center?justify?left?right|class|dir<ltr?rtl|id|lang|onclick|ondblclick|onkeydown|onkeypress|onkeyup|onmousedown|onmousemove|onmouseout|onmouseover|onmouseup|style|title]\';

    // Concatenate 
    $cbnet_valid_elements = $valid_iframe . \',\' . $valid_pre . \',\' . $valid_div;

    // Add to extended_valid_elements if it alreay exists
    if ( isset( $init[\'extended_valid_elements\'] ) ) {
        $init[\'extended_valid_elements\'] .= \',\' . $cbnet_valid_elements;
    } else {
        $init[\'extended_valid_elements\'] = $cbnet_valid_elements;
    }

// Pass $init back to WordPress
    return $init;
}
add_filter(\'tiny_mce_before_init\', \'cbnet_tinymce_config\');