Source

File: wp-includes/class-wp-customize-section.php

public function json() {
		$array                   = wp_array_slice_assoc( (array) $this, array( 'id', 'description', 'priority', 'panel', 'type', 'description_hidden' ) );
		$array['title']          = html_entity_decode( $this->title, ENT_QUOTES, get_bloginfo( 'charset' ) );
		$array['content']        = $this->get_content();
		$array['active']         = $this->active();
		$array['instanceNumber'] = $this->instance_number;

		if ( $this->panel ) {
			/* translators: ▸ is the unicode right-pointing triangle. %s: Section title in the Customizer. */
			$array['customizeAction'] = sprintf( __( 'Customizing ▸ %s' ), esc_html( $this->manager->get_panel( $this->panel )->title ) );
		} else {
			$array['customizeAction'] = __( 'Customizing' );
		}

		return $array;
	}