Registers background image support and renders background styles via render_block filter.

Source: wp-includes/block-supports/background.php
Since: 6.4.0

Support Key

supports.background — top-level boolean/object
supports.background.backgroundImage — checked for render output

Registered Attribute

Only registered if no existing style attribute is defined on the block type.

Block Attributes Used

Values read from $block['attrs']['style']['background']:

Functions

wp_register_background_support()

function wp_register_background_support( WP_Block_Type $block_type )

Since: 6.4.0
Access: private

wp_render_background_support()

function wp_render_background_support( string $block_content, array $block ): string

Since: 6.4.0
Since: 6.5.0 Added backgroundPosition and backgroundRepeat output.
Since: 6.6.0 Removed requirement for backgroundImage.source.
Since: 6.7.0 Added backgroundAttachment output.
Access: private

Processing:

1. Checks block_has_support( $block_type, array( 'background', 'backgroundImage' ), false )
2. Checks wp_should_skip_block_supports_serialization() for backgroundImage
3. If backgroundSize is contain and no position is set, defaults position to 50% 50%
4. Delegates to wp_style_engine_get_styles() for CSS generation
5. Uses WP_HTML_Tag_Processor to inject inline style and has-background class to first tag

Generated CSS

• Inline style attribute with background-image, background-size, background-position, background-repeat, background-attachment
• CSS class: has-background

Hooks

Registration

WP_Block_Supports::get_instance()->register(
    'background',
    array(
        'register_attribute' => 'wp_register_background_support',
    )
);
add_filter( 'render_block', 'wp_render_background_support', 10, 2 );

Note: No apply callback — rendering is handled entirely via the render_block filter.