GC_Block_Type::prepare_attributes_for_render()

	public function prepare_attributes_for_render( $attributes ) {
		// If there are no attribute definitions for the block type, skip
		// processing and return verbatim.
		if ( ! isset( $this->attributes ) ) {
			return $attributes;
		}

		foreach ( $attributes as $attribute_name => $value ) {
			// If the attribute is not defined by the block type, it cannot be
			// validated.
			if ( ! isset( $this->attributes[ $attribute_name ] ) ) {
				continue;
			}

			$schema = $this->attributes[ $attribute_name ];

			// Validate value by JSON schema. An invalid value should revert to
			// its default, if one exists. This occurs by virtue of the missing
			// attributes loop immediately following. If there is not a default
			// assigned, the attribute value should remain unset.
			$is_valid = rest_validate_value_from_schema( $value, $schema, $attribute_name );
			if ( is_gc_error( $is_valid ) ) {
				unset( $attributes[ $attribute_name ] );
			}
		}

		// Populate values of any missing attributes for which the block type
		// defines a default.
		$missing_schema_attributes = array_diff_key( $this->attributes, $attributes );
		foreach ( $missing_schema_attributes as $attribute_name => $schema ) {
			if ( isset( $schema['default'] ) ) {
				$attributes[ $attribute_name ] = $schema['default'];
			}
		}

		return $attributes;
	}