post_categories_meta_box

post_categories_meta_box: 这个函数用来在文章编辑界面上显示类别元框，它允许用户从文章中添加或删除类别。

显示文章类别的表格字段。

function post_categories_meta_box( $post, $box ) {
	$defaults = array( 'taxonomy' => 'category' );
	if ( ! isset( $box['args'] ) || ! is_array( $box['args'] ) ) {
		$args = array();
	} else {
		$args = $box['args'];
	}
	$parsed_args = wp_parse_args( $args, $defaults );
	$tax_name    = esc_attr( $parsed_args['taxonomy'] );
	$taxonomy    = get_taxonomy( $parsed_args['taxonomy'] );
	?>
	<div id="taxonomy-<?php echo $tax_name; ?>" class="categorydiv">
		<ul id="<?php echo $tax_name; ?>-tabs" class="category-tabs">
			<li class="tabs"><a href="#<?php echo $tax_name; ?>-all"><?php echo $taxonomy->labels->all_items; ?></a></li>
			<li class="hide-if-no-js"><a href="#<?php echo $tax_name; ?>-pop"><?php echo esc_html( $taxonomy->labels->most_used ); ?></a></li>
		</ul>

		<div id="<?php echo $tax_name; ?>-pop" class="tabs-panel" style="display: none;">
			<ul id="<?php echo $tax_name; ?>checklist-pop" class="categorychecklist form-no-clear" >
				<?php $popular_ids = wp_popular_terms_checklist( $tax_name ); ?>
			</ul>
		</div>

		<div id="<?php echo $tax_name; ?>-all" class="tabs-panel">
			<?php
			$name = ( 'category' === $tax_name ) ? 'post_category' : 'tax_input[' . $tax_name . ']';
			// Allows for an empty term set to be sent. 0 is an invalid term ID and will be ignored by empty() checks.
			echo "<input type='hidden' name='{$name}[]' value='0' />";
			?>
			<ul id="<?php echo $tax_name; ?>checklist" data-wp-lists="list:<?php echo $tax_name; ?>" class="categorychecklist form-no-clear">
				<?php
				wp_terms_checklist(
					$post->ID,
					array(
						'taxonomy'     => $tax_name,
						'popular_cats' => $popular_ids,
					)
				);
				?>
			</ul>
		</div>
	<?php if ( current_user_can( $taxonomy->cap->edit_terms ) ) : ?>
			<div id="<?php echo $tax_name; ?>-adder" class="wp-hidden-children">
				<a id="<?php echo $tax_name; ?>-add-toggle" href="#<?php echo $tax_name; ?>-add" class="hide-if-no-js taxonomy-add-new">
					<?php
						/* translators: %s: Add New taxonomy label. */
						printf( __( '+ %s' ), $taxonomy->labels->add_new_item );
					?>
				</a>
				<p id="<?php echo $tax_name; ?>-add" class="category-add wp-hidden-child">
					<label class="screen-reader-text" for="new<?php echo $tax_name; ?>"><?php echo $taxonomy->labels->add_new_item; ?></label>
					<input type="text" name="new<?php echo $tax_name; ?>" id="new<?php echo $tax_name; ?>" class="form-required form-input-tip" value="<?php echo esc_attr( $taxonomy->labels->new_item_name ); ?>" aria-required="true" />
					<label class="screen-reader-text" for="new<?php echo $tax_name; ?>_parent">
						<?php echo $taxonomy->labels->parent_item_colon; ?>
					</label>
					<?php
					$parent_dropdown_args = array(
						'taxonomy'         => $tax_name,
						'hide_empty'       => 0,
						'name'             => 'new' . $tax_name . '_parent',
						'orderby'          => 'name',
						'hierarchical'     => 1,
						'show_option_none' => '&mdash; ' . $taxonomy->labels->parent_item . ' &mdash;',
					);

					/**
					 * Filters the arguments for the taxonomy parent dropdown on the Post Edit page.
					 *
					 * @since 4.4.0
					 *
					 * @param array $parent_dropdown_args {
					 *     Optional. Array of arguments to generate parent dropdown.
					 *
					 *     @type string   $taxonomy         Name of the taxonomy to retrieve.
					 *     @type bool     $hide_if_empty    True to skip generating markup if no
					 *                                      categories are found. Default 0.
					 *     @type string   $name             Value for the 'name' attribute
					 *                                      of the select element.
					 *                                      Default "new{$tax_name}_parent".
					 *     @type string   $orderby          Which column to use for ordering
					 *                                      terms. Default 'name'.
					 *     @type bool|int $hierarchical     Whether to traverse the taxonomy
					 *                                      hierarchy. Default 1.
					 *     @type string   $show_option_none Text to display for the "none" option.
					 *                                      Default "&mdash; {$parent} &mdash;",
					 *                                      where `$parent` is 'parent_item'
					 *                                      taxonomy label.
					 * }
					 */
					$parent_dropdown_args = apply_filters( 'post_edit_category_parent_dropdown_args', $parent_dropdown_args );

					wp_dropdown_categories( $parent_dropdown_args );
					?>
					<input type="button" id="<?php echo $tax_name; ?>-add-submit" data-wp-lists="add:<?php echo $tax_name; ?>checklist:<?php echo $tax_name; ?>-add" class="button category-add-submit" value="<?php echo esc_attr( $taxonomy->labels->add_new_item ); ?>" />
					<?php wp_nonce_field( 'add-' . $tax_name, '_ajax_nonce-add-' . $tax_name, false ); ?>
					<span id="<?php echo $tax_name; ?>-ajax-response"></span>
				</p>
			</div>
		<?php endif; ?>
	</div>
	<?php
}