when EVENT "chaining" and variable scope.

You could test this pretty easily:

 
 when HTTP_REQUEST priority 1 { 
  
     This will trigger a runtime TCL error as the variable doesn't exist 
    log local0. "\$non_existent_variable: $non_existent_variable" 
  
     Comment out the above and set the variable in this event 
    set non_existent_variable "now exists!" 
 } 
 when HTTP_REQUEST priority 2 { 
  
     This will work now 
    log local0. "\$non_existent_variable: $non_existent_variable" 
 } 
 

does that make sense? Does the Tcl interp "chain" events together, executing each event independently in a seperate namespace in order of priority, or does it concatenate them all and execute them under the same namespace?

I think each event on the same virtual server is chained together in order of priority under the same namespace.

Obviously, local variables set in each event probably aren't transferrable - that is, I can't access $somevar under a HTTP_RESPONSE event unless it was global when it was declared. But events of the same type fired sequentially.. what happens then?

As cmbhatt said, yes, you can access a local variable across the same TCP connection in different events as long as the event you're referencing the variable in occurs after the local variable was set.

Aaron