Parking the theater domain name on the theatre website seems to have the net effect of being forwarded there. Whether a visitor (or a bot) uses theatre or theater, both URLs will arrive at the same home page.

I had considered putting in a PHP code that would print a short message if the visitor (bot) arrived via the theater URL.

Could/should I put something in robots.txt?

[1] I installed, activated, and configured the Yoast SEO plugin. Next I looked at the source of the home page and found the canonical link in the header. There was lots of other meta properties, such as og. and twitter. (To be explored later.)

[2] I went into cPanel and found I could set up a permanent 301 redirect; I did that, too.

[3] I’m plan to add a brief explanation of theater vs theatre to explain why the domain uses one spelling and the text contains the other spelling. It will go something like this: [Theatre vs Theater? “Theater” is the preferred spelling in American English but some purists still make a distinction between the two words: a theater is a movie/film venue while a theatre is a live performance venue. Our website is theatre, but our content will use “theater” for the benefit of Americans searching Google or Bing.]