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Chris Thilgen 6Chris Thilgen 6 

Error in Trailhead Example

https://developer.salesforce.com/trailhead/force_com_introduction/point_click_business_logic/validation_rules

Website Extension Example includes ".co.uk" in the Error Message section (which the code does not actually check)
SonamSonam (Salesforce Developers) 
Thanks for bringing this up Chris, I will bring this to my team's notice.

As for the formula, I believe adding the line below should help validate this website as well:
RIGHT( Web_Site__c, 6) <> ".CO.UK",
Sandeep BhanotSandeep Bhanot
Thanks for bringing this (and the other great feedback that you've sent our way) to our attention Chris. We'll address these issues ASAP. Thanks
Sandeep Bhanot
Salesforce.com