Xojo casting

Where can I find documentation on casting in Xojo, thanks?

Same place you find most of the other documentation
If its not in that (which is JUST the language reference & not a How To guide)
the its probably in on of the User guides listed on that page
More than likely in the Users Guide Fundamentals in section conveniently named “Casting”

UserGuide-Fundamentals Page 158.

Link to PDF for UserGuide Fundamentals