^((?!-)[a-zA-Z\d-]{1,63}(?<!-)…

^((?!-)[a-zA-Z\d-]{1,63}(?<!-)\.)+[A-Za-z]{2,6}$

Go Haskell Java JavaScript .Net Perl PHP PostgreSQL Python Ruby Tcl XRegExp

https://www.regexplanet.com/share/index.html?share=yyyyfyz7g3r