Registers border-related attributes and generates CSS classes/inline styles for border properties.

Source: wp-includes/block-supports/border.php
Since: 5.8.0

Support Key

supports.__experimentalBorder

Can be set to true (all border features) or an object with individual feature flags:

Registered Attributes

Functions

wp_register_border_support()

function wp_register_border_support( WP_Block_Type $block_type )

Since: 5.8.0
Since: 6.1.0 Improved conditional blocks optimization.
Access: private

wp_apply_border_support()

function wp_apply_border_support( WP_Block_Type $block_type, array $block_attributes ): array

Since: 5.8.0
Since: 6.1.0 Implemented the style engine to generate CSS and classnames.
Access: private

Processing:

1. Checks serialization skip for border
2. For each feature (radius, style, width, color), checks individual feature support and serialization skip
3. Handles both shorthand and per-side (top, right, bottom, left) border values
4. For radius: appends px to numeric values
5. For width: appends px to numeric values
6. For color: uses var:preset|color|{slug} for preset colors, falls back to custom color
7. Delegates to wp_style_engine_get_styles() for CSS generation

Returns: Array with class (classnames) and/or style (inline CSS).

wp_has_border_feature_support()

function wp_has_border_feature_support( WP_Block_Type $block_type, string $feature, mixed $default_value = false ): bool

Since: 5.8.0
Access: private

Returns true if:

• __experimentalBorder is boolean true (all features enabled), OR
• The specific feature flag is set under __experimentalBorder

Block Attributes Read

From $block_attributes['style']['border']:

From $block_attributes['borderColor']: Preset border color slug.

Generated CSS

Via wp_style_engine_get_styles():

• Classnames (e.g. has-border-color)
• Inline styles (e.g. border-radius:5px;border-width:2px;border-color:var(--wp--preset--color--vivid-red))

Registration

WP_Block_Supports::get_instance()->register(
    'border',
    array(
        'register_attribute' => 'wp_register_border_support',
        'apply'              => 'wp_apply_border_support',
    )
);