The block supports subsystem provides server-side rendering of block-level design features (colors, typography, spacing, etc.) by registering attributes, generating CSS classes/inline styles, and injecting them into block markup.

Source: wp-includes/block-supports/
Since: 5.6.0 (earliest files)

Architecture

Each block support file follows a common pattern:

1. Register — A register_attribute callback adds block attributes (e.g. style, backgroundColor) to block types that declare support.
2. Apply — An apply callback reads block attributes and returns CSS classes/inline styles to merge into the block wrapper.
3. Render — Some supports use render_block or render_block_data filters to inject styles via WP_HTML_Tag_Processor for non-server-rendered blocks.

All supports register themselves via WP_Block_Supports::get_instance()->register().

Files Overview

Common Patterns

Serialization Skipping

Blocks can opt out of server-side serialization of specific support features via __experimentalSkipSerialization in their supports definition. The utility function wp_should_skip_block_supports_serialization() (in utils.php) checks this flag. Nearly every apply/render function checks it before generating output.

Style Engine Integration

Most supports delegate CSS generation to wp_style_engine_get_styles(), which returns both classnames and css (inline styles). Supports that generate layout or position CSS use wp_style_engine_get_stylesheet_from_css_rules() to store styles in the style engine for later enqueuing.

WP_HTML_Tag_Processor

Supports that use render_block filters inject classes and inline styles into block markup using WP_HTML_Tag_Processor, targeting the first tag (presumed wrapper element).

Hook Summary

Filters

Actions