Look up a set variable

Look up a set variable

If In my flow I set an arbitrary variable 
Website URL ${website_url}

Is it possible to access the variable "Website URL" in the following scenarios?

  1. Within a custom function (e.g. url= ${website_url} ) ?
  2. As a passed parameter in a custom function (e.g. string custom_function(string website_url, .....)?
  3. Further down the flow diagram ( form input value = ${website_url} )?
Do I need to link it to the flow to be accessible? In other words can it be set and orphaned?