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Gravity Forms is an excellent plugin for adding forms to your WordPress site. It lets you do this easily and quickly and includes many options for functional changes to forms.

For some reason, the plugin does not allow removing the Submit button from its forms, so if you want to use it and embed your own button you will need to remove the plugin’s default button. Add the following line to your functions.php file:

add_filter( 'gform_submit_button', '__return_false' );

For more form customization tips, see Restrict Free Emails in Forms.

By default WordPress allows adding HTML tags in comments such as outbound links, various tags, etc.

Comments do contain rel=nofollow on links automatically, but if you want to completely disable the ability to add any HTML in comments, add the following line to your functions.php file:

add_filter( 'pre_comment_content', 'esc_html' );

WordPress includes functionality that lets you track changes to posts and restore previous versions (Post Revisions). However, these increase the size of the wp_posts table in the database since each revision is another row.

To disable the revision saving functionality in WordPress, add the following line to your wp-config.php file:

define( 'WP_POST_REVISIONS', false);

Alternatively, if you only want to limit the number of revisions saved, add:

define( 'WP_POST_REVISIONS', X);

Replace X with the number of revisions you want to keep.

A very annoying setting – WordPress displays the admin bar to all users logged into the site with their wordpress.com account. To remove the admin bar, add the following line to your functions.php file:

add_filter('show_admin_bar', '__return_false');

This uses a WordPress filter. Learn more about hooks in WordPress Hooks Explained.

WordPress has a built-in function to check if you are on a specific page:

if ( is_page(5) ) {
        // do some stuff
    }

Or whether the page is a child of a specific page:

if ( $post->post_parent == '5' ) {
        // do some stuff
    }

But there is no built-in WordPress function that checks both conditions together, and this is very useful. For example – if we want to load a JS file for a videos page and all pages under it…

The following function (add to functions.php) creates a new logical function for this check:

function is_tree($the_page_id) {   
    global $post;         

    if(is_page()&&($post->post_parent==$the_page_id||is_page($the_page_id))) 
       return true;   
    else 
       return false;   
    };

Usage

if (is_tree(5)) {
        // do some stuff
    }

For more on WordPress page templates, see WordPress Template Hierarchy.

The following code lets you set the default post status on your WordPress site to Private.

<?php 
function default_posts_to_private()
{
	global $post;

	if ( $post->post_status == 'publish' ) {
		$visibility = 'public';
		$visibility_trans = __('Public');
	} elseif ( !empty( $post->post_password ) ) {
		$visibility = 'password';
		$visibility_trans = __('Password protected');
	} elseif ( $post->post_type == 'post' && is_sticky( $post->ID ) ) {
		$visibility = 'public';
		$visibility_trans = __('Public, Sticky');
	} else {
		$post->post_password = '';
		$visibility = 'private';
		$visibility_trans = __('Private');
	} 
?>

	<script type="text/javascript">
		(function($){
			try {
				$('#post-visibility-display').text('<?php echo $visibility_trans; ?>');
				$('#hidden-post-visibility').val('<?php echo $visibility; ?>');
				$('#visibility-radio-<?php echo $visibility; ?>').attr('checked', true);
			} catch(err){}
		}) (jQuery);
	</script>
	<?php
add_action( 'post_submitbox_misc_actions' , 'default_posts_to_private' );

This uses a WordPress hook. Learn more in WordPress Hooks Explained.

When working on a project that requires creating multiple taxonomies, it makes sense to use this function rather than creating a separate function for each taxonomy. Put each taxonomy’s parameters in the array and the function handles the rest:

<?php
/**
 * Register Multiple Taxonomies
 *
 */
function register_multiple_taxonomies() {
    $taxonomies = array(
        array(
            'slug'         => 'job-department',
            'single_name'  => 'Department',
            'plural_name'  => 'Departments',
            'post_type'    => 'jobs',
            'rewrite'      => array( 'slug' => 'department' ),
        ),
        array(
            'slug'         => 'job-type',
            'single_name'  => 'Type',
            'plural_name'  => 'Types',
            'post_type'    => 'jobs',
            'hierarchical' => false,
        ),
        array(
            'slug'         => 'job-experience',
            'single_name'  => 'Min-Experience',
            'plural_name'  => 'Min-Experiences',
            'post_type'    => 'jobs',
        ),
    );
    foreach( $taxonomies as $taxonomy ) {
        $labels = array(
            'name' => $taxonomy['plural_name'],
            'singular_name' => $taxonomy['single_name'],
            'search_items' =>  'Search ' . $taxonomy['plural_name'],
            'all_items' => 'All ' . $taxonomy['plural_name'],
            'parent_item' => 'Parent ' . $taxonomy['single_name'],
            'parent_item_colon' => 'Parent ' . $taxonomy['single_name'] . ':',
            'edit_item' => 'Edit ' . $taxonomy['single_name'],
            'update_item' => 'Update ' . $taxonomy['single_name'],
            'add_new_item' => 'Add New ' . $taxonomy['single_name'],
            'new_item_name' => 'New ' . $taxonomy['single_name'] . ' Name',
            'menu_name' => $taxonomy['plural_name']
        );
        
        $rewrite = isset( $taxonomy['rewrite'] ) ? $taxonomy['rewrite'] : array( 'slug' => $taxonomy['slug'] );
        $hierarchical = isset( $taxonomy['hierarchical'] ) ? $taxonomy['hierarchical'] : true;
    
        register_taxonomy( $taxonomy['slug'], $taxonomy['post_type'], array(
            'hierarchical' => $hierarchical,
            'labels' => $labels,
            'show_ui' => true,
            'query_var' => true,
            'rewrite' => $rewrite,
        ));
    }
    
}
add_action( 'init', 'register_multiple_taxonomies' );

In my last project I needed to split the WordPress loop into groups of three posts – so if there are nine posts, every three would be wrapped in a div. You can do this using a counter and checking inside the loop whether it is a multiple of 3, and if so, closing the div. To change the number of posts per group, change the number 3 on line 14. Here is the code:

<?php if ( have_posts() ) :
	$i = 0;
	while ( have_posts() ) : the_post();
		if ( $i % 3 == 0 ) { ?>
			<div>
	<?php } ?>
			<div class="single_item">
				<h2>
					<a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?>
					</a>
				</h2>
			</div>
	<?php $i ++;
		if ( $i % 3 == 0 ) { ?>
			</div>
	<?php } ?>

	<?php endwhile; ?>
	<?php
	if ( $i % 3 != 0 ) { ?>
		</div>
	<?php } ?>

<?php endif; ?>

For more loop customization, see Remove a Category from the Main Loop.

There are situations (quite common) where you want to limit WordPress search to titles only and not the post body text. To do this, add the following code to your functions.php file. For a more powerful search engine, see Relevanssi Better Search. Note that this function also applies to search performed from the WordPress dashboard.

/**
 * Search SQL filter for matching against post title only.
 *
 * @param   string      $search
 * @param   WP_Query    $wp_query
 */
function wpse_11826_search_by_title( $search, $wp_query ) {
    if ( ! empty( $search ) && ! empty( $wp_query->query_vars['search_terms'] ) ) {
        global $wpdb;

        $q = $wp_query->query_vars;
        $n = ! empty( $q['exact'] ) ? '' : '%';

        $search = array();

        foreach ( ( array ) $q['search_terms'] as $term )
            $search[] = $wpdb->prepare( "$wpdb->posts.post_title LIKE %s", $n . $wpdb->esc_like( $term ) . $n );

        if ( ! is_user_logged_in() )
            $search[] = "$wpdb->posts.post_password = ''";

        $search = ' AND ' . implode( ' AND ', $search );
    }

    return $search;
}

add_filter( 'posts_search', 'wpse_11826_search_by_title', 10, 2 );