Google added eight or so words between brackets to clarify that fields that aren't explicitly listed in the robots.txt documentation aren't supported. Why did they do this? Google said because sometimes Google gets questions about it.
The words Google added were added to the syntax section of the robots.txt documentation and it reads:
(other fields such as crawl-delay aren't supported)
Here is the before and after, where the addition is highlighted in blue:
Here is what it looks like now:
As Jaskaran Singh, Silver Product Expert at Google in Webmaster/Search Console Community, wrote on LinkedIn, "If you're using unsupported fields, like crawl-delay, Google will ignore them. Be sure to follow these supported directives to ensure your site is crawled as intended." He added as "Pro Tip: Always use comments (#) for better readability, and ensure paths start with / to avoid errors."
Forum discussion at LinkedIn.
