I appreciate seeing how you handled the eval for the entire regex expression, escaping two of the tokens to delay their evaluation (I presume). I don't remember having seen that kind of grammar before.
As for the application, my usage involves UTF8 text, and I just provided the example here to simulate the functionality I wish to have. In my own code, what you suggested doesn't seem to work. I'll have to play with it some more later, when I have time again, to see if I can do something more with the grammar you introduced.
The quotes seem to be fine at my end...at least, warnings doesn't indicate any special issue with them. Warnings just says there's an unrecognized escape in the line where I escaped the period and indicated a space with \s. As far as my eye can see, there should be no error there. Useless error messages is why I usually turn warnings off unless I specifically am watching the logs during trouble shooting. Otherwise, my logs just get fat without benefit. In the actual application, the text is coming in from a web form, and is not directly assigned in this manner.