The XOOPS 2.5.11-RC1 release incorporates smarty version 3, prior to this release XOOPS used version 2. The last version (2.6.33) was released in October 2021. Today smarty continues to release versions for the 3.X branch and the 4.X version
For security reasons version 3.1.48 has been integrated into XOOPS 2.5.11 as of RC1, this integration implies changes in the templates as this version is less permissive than version 2.
But what's smarty?
Smarty is a template engine for PHP, facilitating the separation of presentation (HTML/CSS) from application logic.
If you're looking for the documentation for smarty: Smarty documentation
It is likely that when you upgrade to XOOPS 2.5.11-RC1 or higher, your website will show a multitude of errors and nothing will work. Don't worry, by following the different steps described, you should be able to correct all the errors. This operation may take some time, be patient!
To simplify debugging
We have noticed that the error messages are not easily exploitable if you are with a version 8.1.X of php or higher.
To simplify debugging, you need to enable PHP version 7.4.X or 8.0.X.
This is very important, otherwise you will not be able to interpret the error messages and this will make it very difficult to fix.
Another essential point is to activate the debug mode of XOOPS to read the error information!
Control panel / Preferences / General settings / Enable debug : "Enable debug (OnLine mode)"