OR in a regex

From: Colm Gallagher (colm.gallagher_at_gmail.com)
Date: 09/30/04 

Date: Thu, 30 Sep 2004 09:03:55 +0100
To: beginners@perl.org

Hi Folks,

Struggling to understand what is happening here...

Example of text is

Description Supports the management of the process to create and
complete an order Actors SYSTEM Pre-Conditions A Service Instance may
have been selected for the purchase

This regex extracts the text
/Description([^.]+)(?:Actors)/
Supports the management of the process to create and complete an order

In some cases, the word "Actors" that I want to terminate on is the
word "Steps" instead, so I though I'd use an OR inside parenthesis
with no backreferences ?: to match either Actors or Steps - this now
matches neither, so the pattern just runs to the end of the text

  (?<!Change )Description([^.]+)(?:Actors|Steps)

any hints? 

-- 
Colm