I read the regex stuff in the calibre manual, but it didn't do much for me. I don't know what the different parts of the expression mean or do. So I can copy examples from here or there to do things like add series and sort order to title when I send books to my reader, but knowing that X expression does something doesn't help me understand all the parts of the expression in case I want to change it much more than to have my series order a 2-digit number versus a 3-digit one. I'll see what I can find though.
And just for grins, here's "Rambo". He's about 10 weeks old or so.