Validation - prevent html

Yes you can extend the Validation Class.

CodeIgniter 4 User Guide - Creating Custom Rules

You could copy this method ( alpha_numeric_punct ) and work from that.

Thank you.
Do i have to copy the method? I thought i could use the existing functionality and only add my extension. If the method will be updated later i don't have to copy the method again.

I still have a second question: Do some rules depend on the language? I took the alpha Rule, but if i input a czech name like Tomáš the rule fails and i got an error message in my form. I think it is caused by the carachters áš