Source

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

public function branching() {

		/**
		 * Filters whether or not changeset branching is allowed.
		 *
		 * By default in core, when changeset branching is not allowed, changesets will operate
		 * linearly in that only one saved changeset will exist at a time (with a 'draft' or
		 * 'future' status). This makes the Customizer operate in a way that is similar to going to
		 * "edit" to one existing post: all users will be making changes to the same post, and autosave
		 * revisions will be made for that post.
		 *
		 * By contrast, when changeset branching is allowed, then the model is like users going
		 * to "add new" for a page and each user makes changes independently of each other since
		 * they are all operating on their own separate pages, each getting their own separate
		 * initial auto-drafts and then once initially saved, autosave revisions on top of that
		 * user's specific post.
		 *
		 * Since linear changesets are deemed to be more suitable for the majority of WordPress users,
		 * they are the default. For WordPress sites that have heavy site management in the Customizer
		 * by multiple users then branching changesets should be enabled by means of this filter.
		 *
		 * @since 4.9.0
		 *
		 * @param bool                 $allow_branching Whether branching is allowed. If `false`, the default,
		 *                                              then only one saved changeset exists at a time.
		 * @param WP_Customize_Manager $wp_customize    Manager instance.
		 */
		$this->branching = apply_filters( 'customize_changeset_branching', $this->branching, $this );

		return $this->branching;
	}