In addition to working in WordPress, and doing plugin costimization and theme customization, much of which involves the use of PHP – I also worked for years on a site that was 100% custom PHP code. So any change to the outdated php code on the site, or any custom additions to the cart system and more had to be hand coded. I added USPS and UPS integration into the old coding, a discount system, a customer ID system, all by hand, all in the code of that site.