AboutWith this code installed all external links will be marked with the 'No Entry' Unicode character (see attached screenshot).
Internal links explained
An internal link is a type of hyperlink on a webpage to another page or resource, such as an image or document, on the same website or domain.Internal link - Wikipedia
External links examples
Hyperlinks are considered either "external" or "internal" depending on their target or destination. Generally, a link to a page outside the same domain or website is considered external.Internal link - Wikipedia