We is extremely anxious to use a (validated) code with no tabs in it. Tabs, tags and other unnecessary elements doubles and triples the source, and are absolutely intolerable. It makes your site visitors suffer slow page-loading, wich affects its attendance and accessibility.
All software modules are tested on w3C validator, that guarantees the product responds to your requirements. This way of quality control means that the finail testing measures are preliminarily known – before testing, wich saves time and money.