Sometimes, a footnote is common between multiple points in the text. For
example, in a legal/contract document, several clauses are subject to the same
condition (or clarification). In such case, it does not make sense to add a
separate footnote at each point and then repeat the same sentence in the footnote.

Instead, allow the user to insert an EXISTING footnote.

Now this raises a dilemma: If the reader clicks on the hyperlinked number in the
footnote, the cursor normally jumps to the paragraph that refers to it. In this
case, where should it jump (because there are multiple paragraphs that refer to
it)? A workaround is to jump to the top-most paragraph that refers to it, and at
the same time, highlight the "footnote" fields in all the other paragraphs.

Ideally, all the paragraphs that share a common footnote must belong to the same
page, so that the reader does not have to flip pages to look at the footnote.
But in practice, it is OK even if they are a page apart.

If these pages drift apart more than a page, Writer should automatically
replicate the footnote on each page, and renumber the footnotes accordingly.