evaled on page generation

[Andreas]

Only the include statement. Of yourse the included file must aso be parsed/compiled, but as already said files can be cached.

Originally Posted by calorie

Say I make a plugin that sets variable $foo - I am wondering when $foo is first available: a) by plugin and b) by hack.

I don't understand this question, sorry.
What to you want to know - variable scope?
If your plugin is being called from within a function, the any variables you set (if you don't define them as global) will only be visible within this function.
If your plugin is being called from a global scope, then variables will be global.