# What is the reason to put a tilde between “p.”/“page” and the number?

When citing a page, the Biblatex manual puts a tilde between "p."/"page" and the number:

\footcite[Cp.][p.~23]{Smith-2013}


Why? I actually have never really googled for this and now that I have, I am unable to find any good results or think of one.

I recall that I used

\footcite[Cp.][p. 23]{Smith-2013}


a couple of times and I didn't have any problems with the space disappearing or anything. Then I converted back to the tilde method just for the sake of it but did not inquire about it.

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~ is a non-breakable space. –  Gonzalo Medina Mar 22 '14 at 15:07
@GonzaloMedina I am aware of that and this was not my question. –  henry Mar 22 '14 at 15:07
Then what is your question? –  Gonzalo Medina Mar 22 '14 at 15:09
If this question is really about biblatex, do not write \footcite[Cp.][p.~23]{Smith-2013} but \footcite[Cp.][23]{Smith-2013}. If the postnote only contains a number (actually, more specifically, something biblatex recognises as page range), it adds the "page"/"p" prefix and an appropriate space itself. –  moewe Mar 22 '14 at 15:14
biblatex automatically adds a \ppspace between the page prefix ("p."/"page") and the actual page number. \ppspace defaults to \addnbspace, a non-breaking space. (All this can be found in biblatex2.sty.) –  moewe Mar 22 '14 at 15:20

~ is a non-breakable space so no line break will separate the "p." and the number. Not using it might result (if the string "p. #" happens to be close to a lind end) in the string "p." and the number on different lines (even on different pages if "p." is close to a page break) which is not correct.

This is a case of a general rule: when an object is mentioned together with a number (for example, when one cross-references a figure in the form "Figure 5 on page 234"), the object and its associated number must not be separated by a line break. Thus, one has to introduce non-breakable spaces at the proper locations: Figure~\ref{fig:image} on page~\pageref{fig:image}.

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Really, that's it? In the case there was a line break in the footnote, I assume the majority of times the page reference isn't broken. As in, never. I never had that problem. But then... my thought was probably based on pointless egotistical thinking. –  henry Mar 22 '14 at 15:11
@henry The fact that it has not occurred to you up to this moment doesn't rules out the possibility of it happening to someone at some time :) –  Gonzalo Medina Mar 22 '14 at 15:12
Very true... :) –  henry Mar 22 '14 at 15:21
@henry The problem is not so much if you use this in a footnote (\footcite), but if you use \cite, \parencite or \textcite, "p. #" might well hit the end of a line. –  moewe Mar 22 '14 at 15:27
My first comment here seems out of place now. When I posted it there was just the first sentence written in the reply. @moewe that is a good point. –  henry Mar 23 '14 at 7:28

Two things: line breaks and spacing. Without the tilde, TeX an break between 'p.' (or page) and '23' in the example. It's normally considered 'bad style' to have a break here or in any case where you have 'Thing X'-type links. In the specific case of p., as you are using a full stop (period) preceded by a lower case letter, TeX will treat this as an end-of-sentence and may insert extra space (depending on whether \frenchspacing is active). To prevent this you certainly need p.\ 23 even if you want to allow a line break (not a good idea).

Note that depending on the exact nature of your input you may not notice the first issue (of not occurring at a break) or the second (if \frenchspacing is set).

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Interesting. Also, I wasn't aware that it was 'bad style'. –  henry Mar 22 '14 at 15:20