Hi,

Attached is a patch adding a new option
`org-latex-default-class-options'. The option can be set locally (file
locally, buffer locally, etc.) to effect the options which are
interpolated in LaTeX exports by default.

This might not seem terribly useful: if you want to have
standard/common options set for a certain class (or even all classes)
just specify them in the header string in `org-latex-classes'. This is
usually sufficient, but not always.

I have recently been using the LaTeX subfiles package a lot, with org
mode. The package lets your compile multi-file projects in convenient
ways, but (in order to do this) requires that: 1. each subfile uses
the `subfile' class, 2. with the path of the master file passed as an
argument

My workflow is that I have a master file in LaTeX, which includes
various other LaTeX files (which are exports from org files) as
subfiles, thus:

,----
| /project-folder
| ├ main.tex
| ├ chapterOne
| │ ├ chapterone.org
| │ └ chapterone.tex (org export)
| ├ chapterTwo
| │ ├ chaptertwo.org
| │ └ chaptertwo.tex (org export)
| └ chapterThree
|   ├ chapterthree.org
|   └ chapterthree.tex (org export)
`----

Whenever I edit one of the org files, I re-export it, thus updating
the LaTeX subfiles source. So I need that export procedure to fulfil
both 1 and 2 (or,if it doesn't, I have to fiddle with the exported
LaTeX manually, which I don't want to).

Fulfilling 1 is easy---I just set `org-latex-default-class' to
"subfile" in .dir-locals in project-folder (and of course make sure
that "subfile" has a valid class in in `org-latex-classes').

I want to fulfil 2, but I don't want to hardcode `../main.tex', into
my `org-latex-classes', because I might have other projects where the
main file is called something else (or even recursive subfile systems
where different files are the 'main' file at different levels).

At the moment, I solve this by putting:

,----
| #+latex_class_options: [../thesis.tex]
`----

At the top of every org file, but since I do have to this for /every/
file in the hierarchy, it would be nice to get the same effect by just
setting a variable.

So: if I set the newly introduced `org-latex-default-class-options' in
.dir-locals in project-folder, I'll get the right export behaviour
every time and not have to edit the LaTeX manually, /or/ add the
header to each org file manually.

Someone seems to have shown interest in this sort of feature once
before:
<https://emacs.stackexchange.com/questions/29107/org-latex-export-set-default-options-for-documentclass>

best,

Hugo