HTML validator on announcement banner

Problem

Sometimes the customers write an invalid HTML code into their announcement banner, which causes some pages to load improperly. In most cases, Jira simply shows a blank page on the application without throwing any error.
Due to the lack of errors or information about that issue, the customers are unable to identify the problem on their instance which is a time-consuming effort.
An example of that behavior is described on our Advanced Roadmaps Plans not showing issues when an Announcement Banner is present in Jira article.

Suggested Solution

Create an HTML tag validator such as W3 Validator on the Announcement Banner page, to immediately inform the customers that their code is invalid and prevent them to cause failures on Jira. 

Why This Is Important

This could reduce the customer and support efforts to investigate and identify the issue that is happening with the HTML code.
 

Workaround

Get the customer HTML code and check with the W3 Validator or manually.