Final answer:
HTML5 enhances user input in form fields with placeholder text and form validation, which ensure data correctness before submission.
Step-by-step explanation:
The HTML5 additions that are built-in processes designed to check and guide user input into form fields before form submission include placeholder text and form validation. Placeholder text provides a hint or example of the expected input in a form field, which disappears when the user starts typing. Form validation, on the other hand, is a feature that checks whether the data entered by the user conforms to specified formats and meets the criteria set by the attribute types, such as 'email' for email addresses or 'number' for numerical values, before the form can be submitted. This ability to automatically validate user input helps to prevent errors and improve the overall user experience.