Source

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

public function changeset_data() {
		if ( isset( $this->_changeset_data ) ) {
			return $this->_changeset_data;
		}
		$changeset_post_id = $this->changeset_post_id();
		if ( ! $changeset_post_id ) {
			$this->_changeset_data = array();
		} else {
			if ( $this->autosaved() && is_user_logged_in() ) {
				$autosave_post = wp_get_post_autosave( $changeset_post_id, get_current_user_id() );
				if ( $autosave_post ) {
					$data = $this->get_changeset_post_data( $autosave_post->ID );
					if ( ! is_wp_error( $data ) ) {
						$this->_changeset_data = $data;
					}
				}
			}

			// Load data from the changeset if it was not loaded from an autosave.
			if ( ! isset( $this->_changeset_data ) ) {
				$data = $this->get_changeset_post_data( $changeset_post_id );
				if ( ! is_wp_error( $data ) ) {
					$this->_changeset_data = $data;
				} else {
					$this->_changeset_data = array();
				}
			}
		}
		return $this->_changeset_data;
	}