I'm used to using re-entrant code in single php web pages.  It's simpler in a lot of ways, but can someone confirm if VisualForce pages can be used re-entrantly?  (Yes - that's a word - I just made it up).

I used to use PHP SESSION variables to maintain the state of the user process to show or bypass each step of a process and I could do everything in one PHP file (small company)

Very common structure (one php file)

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1) if USER/PWD variables NOT set, show login screen form and die

2) if SEARCH variable not set, show search screen form and die

3) if SELECTED options not set then display Options Form and die

4) Process Selected Option, Show toolbar for related tasks, next steps and die

If I have a VF form with a text search/lookup feature,  what is the best

way to perform the next step in the process?  (step 3)?

Store the results in a class variable?

Pass the results to a separate, unique Visual Force page?

Use the same VF page re-entrantly with conditional / variable processing?

I'm a little confused since the ACTION of a submission button is a Class Method instead of a target web page.  Do I simply include a PageReference in the method and return to the same page and access the variables from the class?