ttrss/plugins/toggle_sidebar/init.php

<?php
class Toggle_Sidebar extends Plugin {

	private $host;

	function about() {
		return array(1.0,
			"Adds a main toolbar button to toggle sidebar",
			"fox");
	}

	function init($host) {
		$this->host = $host;

		$host->add_hook($host::HOOK_MAIN_TOOLBAR_BUTTON, $this);
	}

	function hook_main_toolbar_button() {
		?>

		<button dojoType="dijit.form.Button" onclick="collapse_feedlist()">
			<img src="plugins/toggle_sidebar/application_side_list.png"
				 title="<?php echo __('Collapse feedlist') ?>">
		</button>

		<?php
	}

	function api_version() {
		return 2;
	}

}
?>