WordPress at a glance
function is not described

Walker_PageDropdown::start_el() public WP 2.1.0

Starts the element output.

{} It's a method of the class: Walker_PageDropdown{}

Hooks from the method
Return

null. Nothing.

Usage

$Walker_PageDropdown = new Walker_PageDropdown();
$Walker_PageDropdown->start_el( $output, $page, $depth, $args, $id );
$output(string) (required) (passed by reference — &)
Used to append additional content. Passed by reference.
$page(WP_Post) (required)
Page data object.
$depth(int)
Depth of page in reference to parent pages. Used for padding.
$args(array)
Uses 'selected' argument for selected page to set selected HTML attribute for option element. Uses 'value_field' argument to fill "value" attribute. See wp_dropdown_pages().
Default: empty array
$id(int)
ID of the current page.
Default: 0 (unused)

Notes

Changelog

Since 2.1.0 Introduced.

Code of Walker_PageDropdown::start_el() WP 5.7.2

<?php
public function start_el( &$output, $page, $depth = 0, $args = array(), $id = 0 ) {
	$pad = str_repeat( '&nbsp;', $depth * 3 );

	if ( ! isset( $args['value_field'] ) || ! isset( $page->{$args['value_field']} ) ) {
		$args['value_field'] = 'ID';
	}

	$output .= "\t<option class=\"level-$depth\" value=\"" . esc_attr( $page->{$args['value_field']} ) . '"';
	if ( $page->ID == $args['selected'] ) {
		$output .= ' selected="selected"';
	}
	$output .= '>';

	$title = $page->post_title;
	if ( '' === $title ) {
		/* translators: %d: ID of a post. */
		$title = sprintf( __( '#%d (no title)' ), $page->ID );
	}

	/**
	 * Filters the page title when creating an HTML drop-down list of pages.
	 *
	 * @since 3.1.0
	 *
	 * @param string  $title Page title.
	 * @param WP_Post $page  Page data object.
	 */
	$title = apply_filters( 'list_pages', $title, $page );

	$output .= $pad . esc_html( $title );
	$output .= "</option>\n";
}