Source

File: wp-admin/includes/template.php

function _list_meta_row( $entry, &$count ) {
	static $update_nonce = '';

	if ( is_protected_meta( $entry['meta_key'], 'post' ) ) {
		return '';
	}

	if ( ! $update_nonce ) {
		$update_nonce = wp_create_nonce( 'add-meta' );
	}

	$r = '';
	++ $count;

	if ( is_serialized( $entry['meta_value'] ) ) {
		if ( is_serialized_string( $entry['meta_value'] ) ) {
			// This is a serialized string, so we should display it.
			$entry['meta_value'] = maybe_unserialize( $entry['meta_value'] );
		} else {
			// This is a serialized array/object so we should NOT display it.
			--$count;
			return '';
		}
	}

	$entry['meta_key']   = esc_attr( $entry['meta_key'] );
	$entry['meta_value'] = esc_textarea( $entry['meta_value'] ); // Using a <textarea />.
	$entry['meta_id']    = (int) $entry['meta_id'];

	$delete_nonce = wp_create_nonce( 'delete-meta_' . $entry['meta_id'] );

	$r .= "\n\t<tr id='meta-{$entry['meta_id']}'>";
	$r .= "\n\t\t<td class='left'><label class='screen-reader-text' for='meta-{$entry['meta_id']}-key'>" . __( 'Key' ) . "</label><input name='meta[{$entry['meta_id']}][key]' id='meta-{$entry['meta_id']}-key' type='text' size='20' value='{$entry['meta_key']}' />";

	$r .= "\n\t\t<div class='submit'>";
	$r .= get_submit_button( __( 'Delete' ), 'deletemeta small', "deletemeta[{$entry['meta_id']}]", false, array( 'data-wp-lists' => "delete:the-list:meta-{$entry['meta_id']}::_ajax_nonce=$delete_nonce" ) );
	$r .= "\n\t\t";
	$r .= get_submit_button( __( 'Update' ), 'updatemeta small', "meta-{$entry['meta_id']}-submit", false, array( 'data-wp-lists' => "add:the-list:meta-{$entry['meta_id']}::_ajax_nonce-add-meta=$update_nonce" ) );
	$r .= '</div>';
	$r .= wp_nonce_field( 'change-meta', '_ajax_nonce', false, false );
	$r .= '</td>';

	$r .= "\n\t\t<td><label class='screen-reader-text' for='meta-{$entry['meta_id']}-value'>" . __( 'Value' ) . "</label><textarea name='meta[{$entry['meta_id']}][value]' id='meta-{$entry['meta_id']}-value' rows='2' cols='30'>{$entry['meta_value']}</textarea></td>\n\t</tr>";
	return $r;
}