您可以尝试使用多个regexp仅在尖括号外搜索：

function wpse159789_posts_search( $search, $query ) {
    global $wpdb;
    if ( ! preg_match( \'/\' . $wpdb->posts . \'\\.post_content LIKE \\\'%(.+)%\\\'/\', $search, $matches, PREG_OFFSET_CAPTURE ) ) {
        return $search;
    }
    $search_str = stripslashes( $matches[1][0] );
    // Cater for closed angle pairs embedded in the search string.
    for ( $i = 0, $len = mb_strlen( $search_str ); $i < $len; $i++ ) {
        $q_searches[] = \'(<[^>]*>)?\' . preg_quote( mb_substr( $search_str, $i, 1 ) );
    }
    $q_search = implode( \'\', $q_searches );
    $regexs[] = \'^[^<]*\' . $q_search; // Before any angle bracket.
    $regexs[] = \'(<[^>]*>)[^<]*\' . $q_search; // After any closed angle bracket pair.
    array_unshift( $regexs, implode( \' OR \', array_fill( 0, count( $regexs ), $wpdb->posts . \'.post_content RLIKE %s\' ) ) );
    $search_replace = call_user_func_array( array( $wpdb, \'prepare\' ), $regexs );
    $search = substr( $search, 0, $matches[0][1] ) . $search_replace . substr( $search, $matches[0][1] + strlen( $matches[0][0] ) );
    return $search;
}

我不确定这是否涵盖所有情况，但似乎对有限的测试有效。。。（如果MySQL regexp支持“向后看/向前看”，则会简单得多）。