It's OK, I think I've found the answer to my own question. The # signs bracket the actual regular expression, and the e and the s are modifiers - e is equivalent to PREG_REPLACE_EVAL and  s is equivalent to PCRE_DOTALL. Maybe these are things which are so familiar to the experienced players that they almost go without saying, but ...

I have the following regex statement I'm trying to run in PHP.  (?<!(end\s?zone|lower|upper)\s?)(view)  Testing against the following string: (matches in bold) "The endzone view goes hi upper view and he goes view and then goes view and view and view!!!" Notice "upper view" and "endzone view" are ...