/Perl M[ou]ngers/    # char class version
    /Perl M(o|u)ngers/   # alternation version

##</code><code>##

    Perl Mongers
    Perl Mungers
    Perl Monks

##</code><code>##

    Perl Munks
    Perl Mungs
    Perl Mongs
    Perl Monkers
    Perl Munkers

##</code><code>##

   ( /Perl M[ou]ngers/ || /Perl Monks/ )
     /Perl (?:M[ou]ngers|Monks)/

##</code><code>##

        /Perl M(?:onk|[ou]nger)s/

##</code><code>##

    /Perl M(?:(o)|(u))n(?(2)(g)|(?:(g)|(k)))(?(5)|er)s/;