JHtml::_('stylesheet', 'path/to/your/stylesheet.css', array(), true);
JHtml::_('script', 'path/to/your/script.js', array(), true);
JHtml::_('script', 'raw', "alert('Hello World!');");This code will allow you to register any custom script into your Joomla website. You should use the "raw" parameter to indicate your script as a string. In conclusion, JHtml register is a Joomla Platform library that allows developers to register assets like stylesheets, JavaScript files or custom scripts. This library is part of the Joomla Platform and its package library is "joomla/html".