You're on the way to growing your market share
with an Accessible ADA Compliant Website.
Robust Operational Platform
A Robust Platform involves coding practices that work without a browser correcting errors. 
4.1.1 Use Good, Clean Code
Your website should comply with best practices and standards for coding.  Any significant errors in code should be fixed.
This is a very broad and sweeping requirement. It makes sure that browsers, screen readers, and other assistive technologies can analyze and make your website’s code understandable (“parse” is the technical word) so that your website is rendered correctly.
Many browsers can go past errors and still render a website correctly but it’s bad practice to rely on browsers and assistive technologies to interpret incorrect code.

4.1.2 Custom Components Are Accessible

For all user interface components (e.g. forms, links, scripts, controls, etc.), the name and role of those components is coded in.  Also, any states, properties, and values set by the user can be programmatically updated so browsers and assistive technologies are aware of and reflect changes.
This success criterion applies specifically for custom components such as ones a developer has created or from third party vendors.