^$
Finds an empty paragraph.
$ or $0
Adds the string that was found by the search criteria in the Search for box to the term in the Replace with box when you make a replacement.
For example, if you enter "window" in the Search for box and "&frame" in the Replace with box, the word "window" is replaced with "windowframe".
You can also enter an "&" in the Replace with box to modify the Attributes or the Format of the string found by the search criteria.
https://help.libreoffice.org/4.4/Common/List_of_Regular_Expressions
