UBB.threads PHP Forum Software Community Forums Resources and Customizing How Do I? PHP Variable Scope on Included Code

I'm creating a small class in
Control Panel > Display > General > Default Header

When I use this class in
Control Panel > Content > Forums > Forum Introduction Body

The class is "not found".

I tried making a static class (having all static members) and it was also not found.

Wouldn't the static class be globally available during the entire request?

How can I create a globally-available class for inserting some custom code?

Thanks in advance for help