Website Standards
Every website which is built should not only meet the customers standards but must adhere to other standards. Some of the standard which website should be built to are W3C, DDA and Companies House. For a website to be built and meet diferent standard will help the improvement on the search engines, so if the coding has errors then the search engines are not going to place your website as high on the them.
Find below some links which will help you and guide you about the standards which are covered when building a website.
W3C Validation WebsiteDDA Compliance WebsiteCompanies House WebsiteWeb Accessibility Guidelines Website