Navigation walker classes in Wordpress - Step-by-Step Execution

Concept Flow - Navigation walker classes

Start WordPress Menu

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Call Walker Class

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Walker::start_lvl()

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Walker::start_el()

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Generate HTML for Menu Item

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Walker::end_el()

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Walker::end_lvl()

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Return Complete Menu HTML

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Display Menu

WordPress calls the walker class methods in order to build the menu HTML step-by-step.

Execution Sample

Wordpress

<?php
class My_Walker extends Walker_Nav_Menu {
  function start_el(&$output, $item, $depth=0, $args=null, $id=0) {
    $output .= '<li>' . $item->title;
  }
}

This code defines a custom walker that adds a simple list item with the menu item's title.

Execution Table

Step	Method Called	Input	Action	Output
1	start_lvl	depth=0	Add <ul> tag for submenu start	<ul>
2	start_el	item=Home	Add <li> with item title	<ul><li>Home
3	end_el	item=Home	Close <li> tag	<ul><li>Home</li>
4	start_el	item=About	Add <li> with item title	<ul><li>Home</li><li>About
5	end_el	item=About	Close <li> tag	<ul><li>Home</li><li>About</li>
6	end_lvl	depth=0	Close <ul> tag	<ul><li>Home</li><li>About</li></ul>
7	Return	Complete HTML	Return full menu HTML	<ul><li>Home</li><li>About</li></ul>

💡 All menu items processed, submenu levels closed, menu HTML complete.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
$output	""	"<ul><li>Home"	"<ul><li>Home</li>"	"<ul><li>Home</li><li>About"	"<ul><li>Home</li><li>About</li>"	"<ul><li>Home</li><li>About</li></ul>"	"<ul><li>Home</li><li>About</li></ul>"

Key Moments - 2 Insights

Why does start_el add the opening <li> but end_el adds the closing </li>?

Because start_el begins the menu item HTML and end_el finishes it, keeping HTML tags balanced as shown in steps 2 and 3.

What happens if end_lvl is not called?

The submenu <ul> tag would remain open, causing invalid HTML. Step 6 shows end_lvl closing the <ul> properly.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of $output after step 4?

A "<ul><li>Home<li>About"

B "<ul><li>Home</li><li>About"

C "<ul><li>Home</li><li>About</li>"

D "<li>Home</li><li>About"

💡 Hint

Check the output column at step 4 in the execution_table.

At which step does the submenu <ul> tag get closed?

A Step 3

B Step 2

C Step 6

D Step 5

💡 Hint

Look for end_lvl method call in the execution_table.

If start_el did not add the opening <li> tag, what would happen to the menu HTML?

A Menu items would not be wrapped in list items

B Submenu <ul> tags would not open

C Menu would have extra closing </li> tags

D Menu would not display any titles

💡 Hint

Refer to the action column in steps 2 and 4 in the execution_table.

Concept Snapshot

Navigation walker classes build WordPress menus step-by-step.
They use methods like start_lvl, start_el, end_el, end_lvl.
start_el adds opening <li> and content; end_el closes <li>.
start_lvl and end_lvl wrap submenu items in <ul> tags.
Custom walkers let you change menu HTML structure easily.

Full Transcript

Navigation walker classes in WordPress control how menus are built in HTML. The process starts by calling the walker class, which runs methods in order: start_lvl to open submenu lists, start_el to add each menu item with an opening <li> tag and title, end_el to close each <li>, and end_lvl to close submenu lists. This step-by-step method ensures valid HTML structure. The output variable accumulates the HTML as each method adds parts. If any method is missing or incorrect, the menu HTML can break. Custom walker classes let developers change how menus look by overriding these methods.