The purpose of this success criteria is to allow assistive technologies to interpret and parse content. If content is poorly coded the user will have trouble viewing it, navigating it, or not be able to see it at all.
Parsing is to analyze a string or text into logical syntactic components. Proper coding will allow assistive technologies to put your content into easy to navigate formation.
A mismatched attribute or closing bracket will not meet the success criteria.
HubSpot will alert you when there is an error.