What is PHP?
PHP is a widely-used general-purpose scripting language that is particularly well suited for web development and embedded within HTML. Rather than using lots of commands to output HTML (as with C or Perl), PHP pages contain HTML with embedded code that accomplishes a task (in this case, "Hello, I'm a PHP script! "). It is important to note that PHP differs from client-side JavaScript in that the code is executed on the server, which generates HTML, which is then sent to the client. Although the client would receive the results of running that script, they would not know the underlying code. In addition, you can configure your webserver to process all your HTML files using PHP, so your users will be unable to discover what you are doing behind the scenes. There are several advantages to using PHP, including that it is straightforward to use for a newcomer but offers a range of advanced features for professional programmers.
PHP JXL support
PHP has recently added support for AVIF in version 8.1. To this date, no native PHP support is available. Luckily, Johannes Siipola has created a PHP library for encoding JPEG XL images. It requires PHP 7.2.5 or later and works under Linux, macOS, or Windows OS with x64 architecture. Check out the plugin and the installation guide right on his Github page.