Classic Theme Sidebars and Widgets

Use this when adding or reviewing widget areas in a classic PHP theme: blog sidebars, footer columns, header widget areas, shop sidebars, or template-specific widget regions.

In WordPress naming, "sidebar" means a registered widget area. It does not have to appear visually at the side of the layout.

When to Use This Skill

• Registering widget areas with register_sidebar().
• Creating sidebar.php or sidebar-{name}.php.
• Rendering dynamic_sidebar().
• Checking empty widget area behavior.
• Migrating hardcoded footer/header content to user-manageable widget areas.
• Reviewing widget markup semantics and REST exposure.

Register Widget Areas

Register widget areas on widgets_init.

add_action( 'widgets_init', 'mytheme_register_sidebars' );

function mytheme_register_sidebars() {
	register_sidebar(
		array(
			'name'          => __( 'Primary sidebar', 'textdomain' ),
			'id'            => 'sidebar-1',
			'description'   => __( 'Widgets shown beside the main content.', 'textdomain' ),
			'before_widget' => '<aside id="%1$s" class="widget %2$s">',
			'after_widget'  => '</aside>',
			'before_title'  => '<h2 class="widget-title">',
			'after_title'   => '</h2>',
			'show_in_rest'  => false,
		)
	);
}

Rules:

• Always provide an explicit id.
• Treat IDs as persistent storage keys. Changing an ID after release can orphan assigned widgets.
• Keep %1$s and %2$s in before_widget; core substitutes widget ID and classes.
• Choose semantic wrappers: aside for side content, section for content regions, div only when no semantic element fits.
• Use translated name and description.
• register_sidebar() adds theme support for widgets.

Multiple Areas

Use predictable IDs for repeated footer columns.

for ( $i = 1; $i <= 4; $i++ ) {
	register_sidebar(
		array(
			'name'          => sprintf(
				/* translators: %d: Footer column number. */
				__( 'Footer column %d', 'textdomain' ),
				$i
			),
			'id'            => 'footer-' . $i,
			'before_widget' => '<section id="%1$s" class="widget %2$s">',
			'after_widget'  => '</section>',
			'before_title'  => '<h2 class="widget-title">',
			'after_title'   => '</h2>',
		)
	);
}

Rules:

• Keep generated IDs stable.
• Use translator comments for numbered names.
• Do not let Customizer options or request values create arbitrary sidebar IDs.

Render a Sidebar

Use is_active_sidebar() before outputting layout wrappers.

if ( is_active_sidebar( 'sidebar-1' ) ) :
	?>
	<aside id="secondary" class="widget-area" aria-label="<?php esc_attr_e( 'Sidebar', 'textdomain' ); ?>">
		<?php dynamic_sidebar( 'sidebar-1' ); ?>
	</aside>
	<?php
endif;

Rules:

• Do not output empty wrapper markup for inactive sidebars unless the layout requires a placeholder.
• Pass the sidebar ID, not a translated name.
• Do not hardcode widget output in the theme to simulate a widget area.
• dynamic_sidebar() returns a boolean; use it if you need fallback behavior.

Sidebar Template Files

Use get_sidebar() to load sidebar template files.

get_sidebar();          // sidebar.php
get_sidebar( 'footer' ); // sidebar-footer.php

Rules:

• Put reusable sidebar rendering in sidebar.php or sidebar-{name}.php.
• Keep registration in functions.php/inc/widgets.php, not in sidebar templates.
• Do not make sidebar templates query-heavy; they may appear on many pages.

REST and Block Widget Era

register_sidebar() supports show_in_rest.

Rules:

• Leave show_in_rest => false unless the widget area must be exposed publicly through REST.
• If enabling REST exposure, assume the sidebar structure is public data.
• Classic themes can still render widget areas with dynamic_sidebar() even when the admin widget UI uses block widgets.
• Do not disable block widgets just because the theme is classic unless the project has a tested compatibility reason.

Markup and Accessibility

Good widget-area output:

• Uses a landmark or labeled region when it is a major page area.
• Does not create many unlabeled aside landmarks.
• Keeps heading levels sensible for the template context.
• Lets individual widgets output their own content.

Wrapper choice examples:

Area	Wrapper
Blog sidebar	<aside class="widget-area">
Footer column	<section class="footer-widget-area">
Header utility area	<div class="header-widget-area"> or labeled <aside>

Theme vs Plugin Boundary

Themes may register display regions. Plugins should register reusable widgets that provide business functionality.

Good theme-owned widget areas:

• Sidebar.
• Footer columns.
• Header utility region.
• Homepage display sections.

Bad theme-owned functionality:

• CRM signup logic.
• Payment/account widgets.
• Custom data dashboards.
• Anything that must survive theme switching.

Review Checklist

• Widget areas are registered on widgets_init.
• Every sidebar has an explicit stable id.
• Widget wrappers preserve %1$s and %2$s.
• Titles use appropriate heading levels.
• Template output checks is_active_sidebar() before printing layout wrappers.
• dynamic_sidebar() receives IDs, not translated names.
• Empty widget areas do not leave broken layout gaps.
• show_in_rest is intentional.
• Business widgets are not implemented inside the theme.

Common Mistakes

• Omitting id and relying on generated sidebar-1 notices.
• Renaming a sidebar ID after users have assigned widgets.
• Removing %1$s or %2$s from before_widget.
• Rendering empty <aside> containers on every page.
• Registering sidebars from template files.
• Using widget areas as plugin data storage.

References

• Official documentation: https://developer.wordpress.org/themes/classic-themes/functionality/sidebars/
• Official documentation: https://developer.wordpress.org/themes/classic-themes/functionality/widgets/
• Official documentation: https://developer.wordpress.org/reference/functions/register_sidebar/
• Official documentation: https://developer.wordpress.org/reference/functions/dynamic_sidebar/
• Verified source paths:
  • wp-includes/widgets.php
  • wp-includes/theme.php
  • wp-includes/general-template.php
  • wp-content/themes/storefront/sidebar.php
  • wp-content/themes/storefront/inc/class-storefront.php
  • wp-content/themes/generatepress/sidebar.php
  • wp-content/themes/generatepress/inc/general.php