I am new to using sed but I have been experimenting sed's s/..../..../ (substitute) to modify a full sentence if it's on one line but I am unaware an alternative solution on how to modify a sentence that may have been separated on two lines such as:

This:

Lorem Ipsum is simply dummy text of the printing and typesetting industry.

is actually written as this:

Lorem Ipsum is simply dummy text of the 

printing and typesetting industry.

How can you detect for this or code it to replace the entire sentence even if it's on two lines instead of one?