Source

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

public function __construct( $manager, $id, $args = array() ) {
		$keys = array_keys( get_object_vars( $this ) );
		foreach ( $keys as $key ) {
			if ( isset( $args[ $key ] ) ) {
				$this->$key = $args[ $key ];
			}
		}

		$this->manager = $manager;
		$this->id      = $id;

		// Parse the ID for array keys.
		$this->id_data['keys'] = preg_split( '/\[/', str_replace( ']', '', $this->id ) );
		$this->id_data['base'] = array_shift( $this->id_data['keys'] );

		// Rebuild the ID.
		$this->id = $this->id_data['base'];
		if ( ! empty( $this->id_data['keys'] ) ) {
			$this->id .= '[' . implode( '][', $this->id_data['keys'] ) . ']';
		}

		if ( $this->validate_callback ) {
			add_filter( "customize_validate_{$this->id}", $this->validate_callback, 10, 3 );
		}
		if ( $this->sanitize_callback ) {
			add_filter( "customize_sanitize_{$this->id}", $this->sanitize_callback, 10, 2 );
		}
		if ( $this->sanitize_js_callback ) {
			add_filter( "customize_sanitize_js_{$this->id}", $this->sanitize_js_callback, 10, 2 );
		}

		if ( 'option' === $this->type || 'theme_mod' === $this->type ) {
			// Other setting types can opt-in to aggregate multidimensional explicitly.
			$this->aggregate_multidimensional();

			// Allow option settings to indicate whether they should be autoloaded.
			if ( 'option' === $this->type && isset( $args['autoload'] ) ) {
				self::$aggregated_multidimensionals[ $this->type ][ $this->id_data['base'] ]['autoload'] = $args['autoload'];
			}
		}
	}