wp_get_layout_definitions() │ WP 6.3.0

Returns layout definitions, keyed by layout type.

Provides a common definition of slugs, classnames, base styles, and spacing styles for each layout type. When making changes or additions to layout definitions, the corresponding JavaScript definitions should also be updated.

Internal function — this function is designed to be used by the kernel itself. It is not recommended to use this function in your code.

No Hooks.

Returns

Array[]. Layout definitions.

Usage

wp_get_layout_definitions();

Changelog

Since 6.3.0 Introduced.
Since 6.6.0 Updated specificity for compatibility with 0-1-0 global styles specificity.

wp_get_layout_definitions() code WP 6.9.1

wp-includes/block-supports/layout.php 
function wp_get_layout_definitions() {
	$layout_definitions = array(
		'default'     => array(
			'name'          => 'default',
			'slug'          => 'flow',
			'className'     => 'is-layout-flow',
			'baseStyles'    => array(
				array(
					'selector' => ' > .alignleft',
					'rules'    => array(
						'float'               => 'left',
						'margin-inline-start' => '0',
						'margin-inline-end'   => '2em',
					),
				),
				array(
					'selector' => ' > .alignright',
					'rules'    => array(
						'float'               => 'right',
						'margin-inline-start' => '2em',
						'margin-inline-end'   => '0',
					),
				),
				array(
					'selector' => ' > .aligncenter',
					'rules'    => array(
						'margin-left'  => 'auto !important',
						'margin-right' => 'auto !important',
					),
				),
			),
			'spacingStyles' => array(
				array(
					'selector' => ' > :first-child',
					'rules'    => array(
						'margin-block-start' => '0',
					),
				),
				array(
					'selector' => ' > :last-child',
					'rules'    => array(
						'margin-block-end' => '0',
					),
				),
				array(
					'selector' => ' > *',
					'rules'    => array(
						'margin-block-start' => null,
						'margin-block-end'   => '0',
					),
				),
			),
		),
		'constrained' => array(
			'name'          => 'constrained',
			'slug'          => 'constrained',
			'className'     => 'is-layout-constrained',
			'baseStyles'    => array(
				array(
					'selector' => ' > .alignleft',
					'rules'    => array(
						'float'               => 'left',
						'margin-inline-start' => '0',
						'margin-inline-end'   => '2em',
					),
				),
				array(
					'selector' => ' > .alignright',
					'rules'    => array(
						'float'               => 'right',
						'margin-inline-start' => '2em',
						'margin-inline-end'   => '0',
					),
				),
				array(
					'selector' => ' > .aligncenter',
					'rules'    => array(
						'margin-left'  => 'auto !important',
						'margin-right' => 'auto !important',
					),
				),
				array(
					'selector' => ' > :where(:not(.alignleft):not(.alignright):not(.alignfull))',
					'rules'    => array(
						'max-width'    => 'var(--wp--style--global--content-size)',
						'margin-left'  => 'auto !important',
						'margin-right' => 'auto !important',
					),
				),
				array(
					'selector' => ' > .alignwide',
					'rules'    => array(
						'max-width' => 'var(--wp--style--global--wide-size)',
					),
				),
			),
			'spacingStyles' => array(
				array(
					'selector' => ' > :first-child',
					'rules'    => array(
						'margin-block-start' => '0',
					),
				),
				array(
					'selector' => ' > :last-child',
					'rules'    => array(
						'margin-block-end' => '0',
					),
				),
				array(
					'selector' => ' > *',
					'rules'    => array(
						'margin-block-start' => null,
						'margin-block-end'   => '0',
					),
				),
			),
		),
		'flex'        => array(
			'name'          => 'flex',
			'slug'          => 'flex',
			'className'     => 'is-layout-flex',
			'displayMode'   => 'flex',
			'baseStyles'    => array(
				array(
					'selector' => '',
					'rules'    => array(
						'flex-wrap'   => 'wrap',
						'align-items' => 'center',
					),
				),
				array(
					'selector' => ' > :is(*, div)', // :is(*, div) instead of just * increases the specificity by 001.
					'rules'    => array(
						'margin' => '0',
					),
				),
			),
			'spacingStyles' => array(
				array(
					'selector' => '',
					'rules'    => array(
						'gap' => null,
					),
				),
			),
		),
		'grid'        => array(
			'name'          => 'grid',
			'slug'          => 'grid',
			'className'     => 'is-layout-grid',
			'displayMode'   => 'grid',
			'baseStyles'    => array(
				array(
					'selector' => ' > :is(*, div)', // :is(*, div) instead of just * increases the specificity by 001.
					'rules'    => array(
						'margin' => '0',
					),
				),
			),
			'spacingStyles' => array(
				array(
					'selector' => '',
					'rules'    => array(
						'gap' => null,
					),
				),
			),
		),
	);

	return $layout_definitions;
}