Is it possible to have footnotes which are paragraphed according to the following rule (common in my discipline, history)?
Footnotes always begin on a new line, unless there is sufficient whitespace following the previous footnote to fit the entire footnote.
Thus: a) short footnotes can be paragraphed following a multi-line footnote, provided there is sufficient blank space; and b) footnotes which do not begin at the left margin (i.e. which are paragraphed following another footnote) can never run onto the following line.
Here is an example of effect (a): short footnotes paragraphed after multi-line footnotes:
Effect (b) is harder to illustrate (as it is proving a negative), but as far as I can tell, in historical monographs published by (for example) Oxford University Press or Cambridge University Press, footnotes are never set in the position of footnotes 3 or 5 in the image above if they would then run onto the following line—even if setting them that way would save on the total vertical space the footnote block requires.
As far as I can tell, the bigfoot package paragraphs footnotes according to two rules: 1. Footnotes which are more than one line long are not paragraphed with anything, preceding or following. 2. That condition satisfied, set the footnotes in whatever way will minimize the vertical space required.
(This may be wrong; it is just based on observed effects.)
So, for example, this:
\documentclass{article}
\usepackage[para]{bigfoot}
\DeclareNewFootnote[para]{default}
\begin{document}
The first sentence.\footnote{This is a long footnote, to show that short footnotes are not paragraphed following multiline footnotes.}
The second sentence.\footnote{A short footnote.}
The third sentence.\footnote{This is a somewhat longer footnote, to show that it is allowed to overrun the line.}
The third sentence.\footnote{This is another short footnote.}
\end{document}
Renders as this, for me:
I would want 'Footnote 2' to be in the whitespace following 'Footnote 1'. And if 'Footnote 2' were placed as it is, then 'Footnote 3' would not be paragraphed following it, as it runs into the next line.
The second (b) effect which I want can be done manually with 'post-processing' by changing any footnote which runs over like that to be \footnote+{Example text.}, which forces it onto its own line. But that has to be done as the very last thing, as it changes pagination and cross-references. footmisc will achieve effect (a), but only by running all footnotes together as a single paragraph, which is not the goal.
Finally, in an ideal solution, any footnotes placed together on a line would be spread as far apart as possible, or at least have substantial whitespace left (as in the first picture above).
Best Answer
I started with your picture, i.e. footnotes begin at the left margin or in the middle.
I can show how this can be done in plain TeX. If you are using different macro package then you can inspire by this code and re-implement it to your favorite macro package.
The code (you can try it by the command
tex test.tex):The result:
The notes to the implementation: Each footnote text is saved to the control sequence
\specfoot:\the\specfootnumwhich is unique in the whole document. The raw calculation about the vertical space of such footnote is done when\footnotemacro is processed. The result is\dimen0which is inserted to the\insertas\vbox to\dimen0{\vss\penalty\specfootnum}. This means that the real text isn't saved to the\footinsbox. Only empty box with the "message" about the number of the footnote is icluded here.What does
\outputroutine? It creates the list of numbers of the footnotes at the current page, because the\penaltiesinside boxes are read. The list of current footnotes are set to the\tmpmacro. Then the typesetting of these footnotes is processed using control sequences\specfoot:\the\specfootnum. Printing of each footnote is ended by measurement of the text in the last line using\newdimenonemacro. The result is set to the\dimen1. If\dimen1<.5\hsizeand the width of the next footnote is less than.5\hsizethen this next footnote is started by\vskip-\baselineskipand\hskip.5\hsize.