Is that intended as an improvement? What purpose does the \G serve?

#perl -l
for(
    'sue,fred,x(mary,jane)',
    'x(a,b),c(d,e,f),g,h,i(j,k)',
    'a,b,cdef(g),h,i(j)',
    'a,b,c(d(e,f,g)),h,i(j)'
) {
    print join' | ', m/( [^,(]+ \( [^)]+ \) | [^,]+ )(?:$|,)/gx;
    print join' | ', m/( [^,()]+ \( [^()]+ \) | [^,()]+ )(?:$|,)/gx;
    print join' | ', m/\G( [^,()]* \( [^()]* \) | [^,()]+ )(?:,|$)/gxc
+;
    if(  length != pos  ) {
        warn "Invalid input: $_\n";
    }
    print '';
};;

...

a | b | c(d(e | f | g)) | h | i(j)
a | b | e | f | h | i(j)
a | b
Invalid input: a,b,c(d(e,f,g)),h,i(j)
[download]