As the Google crawler is a just a basic HTML parser, it makes sense that certain errors could cause major problems for a site — messed up nesting, missing quote

As the Google crawler is a just a basic HTML parser, it makes sense that certain errors could cause major problems for a site — messed up nesting, missing quotes, etc. Google likely has fairly sophisticated error recovery in place, but I'm sure it doesn't cover everything. As such, it's always to one's advantage to validate their site in order to minimize friction.