Wow! This works!

I actually tried "correcting" what you had there, thinking you'd made a mistake, as it was so simple, i.e., it appeared you'd forgotten the "->()" after "$replace" and the "e" at the end. (I guess I was making this all harder than it needed to be.) Of course, my corrections did not work. Then I took a closer look and realized you had eliminated those evaluated subroutines altogether. I felt like it couldn't possibly work that way, but, went ahead and tried it anyhow. I'm very surprised at how well it works, and I'm not sure why it does work so well. I guess I need to learn more about using eval as a wrapper around a substitution regex. It's highly likely this would have been useful for me in a number of my past projects.

Thank you ever so much for taking time to offer your corrections.

It may be worthy of mention that in my actual code, I am not using any of the quotes such as the qr'(St\.\s)(Mt\.\s)(?=Helens)'; because the variables are coming in straight from the form, with the exception of the untainting routine that the substitution side passes through. So escaped characters were never a part of my issue. The difficulty seems to have been with the complexity of the nested eval.