Templating changes in 2021.10.0

Thank you @petro and @123 you both have been very helpful in getting me through this learning curve. I am finally starting to understand what each line means in the template (still making mistakes) but getting there. This site has help me

https://jinja.palletsprojects.com/en/2.10.x/templates/#forceescape

I still don’t understand some of the arguments. Is HA using a combination of Python / Jinja for what is allowed? For example I had used the word multiply in my template ( must have copied it from someones code) and I can’t understand why instead of just using " * ". Where can I get more information on “allowed” operations?