LaTeX Reader: Allow environments other than "document" while parsing header

[smheidrich]

For example, allow the filecontents environment (see ltclass.dtx for a description) before \begin{document}.

Test case:

filecontents_test.latex

\documentclass[a4paper,12pt]{article}
\begin{filecontents}{blubb.txt}
File text.
\end{filecontents}
\begin{document}
Document text.
\end{document}

Try to convert this to LaTeX (e.g. when you just want to use the --filter facility) or anything else:

pandoc --standalone --parse-raw --from latex --to latex filecontents_test.latex -o filecontents_test_output.latex

Output is:

pandoc: 
Error at "source" (line 2, column 7):
unexpected "f"
expecting "{document}"
\begin{filecontents}{blubb.txt}
      ^

---

Expected output was:

• Pandoc executes without errors.
• filecontents_test_output.latex contains the filecontents environment from filecontents_test.latex in its header.
• When translating to anything other than LaTeX, the environment is ignored instead.

---

Version info:

pandoc 1.12.3.3

---

The filecontents environment is just an example and very low-priority since almost nobody uses it. However, its existence means the Reader's assumption that the only environment that can be opened from the header is document might be wrong.