Changing variable values in one class from another class

I have two document classes. One is Main.as the other is Step2.as. I want to declare a public variable in Main.as then need to give it a value from Step2.as. That value will later be used in my next Document class Step3.as How would I write the code that gives the value in my Step2.as and then how would I write the code that retrieves the value in my Step3.as?

Note I can’t import my Step2/ or Step3 document class into my Main.as. Thanks in advance guys.