Module markdown 

The Kernsetzer Markdown dialect (M1 extends the M0 subset, see checklist).

Title: Der Leuchtturm          <- front matter: `Key: value` lines at the top
Author: Lena Brandt               keys: Title, Subtitle, Author, Lang,
Lang: de                          Publisher, Copyright (or Rights),
                                  Dedication; or a YAML block between
                                  `---` lines (see `front_matter.rs`).
                                  Without `Lang:`, English or German is
                                  detected from the text, as for .docx

*For Ada, who asked first.*    <- before the first heading: a paragraph
                                  starting like a dedication (For, To, Für,
                                  In memory, Gewidmet, …) is a Dedication
                                  section; up to three more right after it
                                  join it, 300 characters in all. Italic
                                  over a whole paragraph is dropped

# Chapter title                <- new chapter
# Prolog / # Prologue          <- recognized section kinds (also Epilog, …)
# Interlude {-}                <- an unnumbered chapter (also `{.unnumbered}`,
                                  as in Pandoc): no label, counting skips it
## Subheading                  <- heading inside the section; `##` is level 1,
                                  `###` level 2, … up to `######`

> Quoted text, lines joined.   <- block quote; a bare `>` line separates
>                                 paragraphs, a blank line ends the quote
> Second paragraph.

Paragraphs are separated by blank lines. *Emphasis*, _emphasis_, **strong**,
[small caps]{.smallcaps} (a Pandoc span; other `{…}` attributes are dropped),
2^nd^, H~2~O (superscript, subscript: no spaces inside, `~~` is text),
[links](https://example.com "title") and <https://example.com>.

Dear Anna,\                    <- a trailing `\` is a line break (paragraphs,
the house is sold.                quotes, notes); on a last line it is dropped

:::verse                       <- verse: every line is kept, a trailing `\`
How doth the little crocodile     is allowed; blank lines separate stanzas;
    Improve his shining tail,     ends at `:::` (or, with a warning, before
                                  the next heading or at the end). Leading
How cheerfully he seems to grin,  spaces indent a line: one level per four
:::                               (a tab is four), counted from the least-
                                  indented line, up to six levels

:::epigraph                    <- epigraph: text joined like a paragraph
Every coast is a rumour\          (blank lines become line breaks); a last
until someone draws it twice.     line starting with a dash is the
— Harbour saying                  attribution, plain text. After a `#`
:::                               heading: the section's epigraph; before
                                  the first heading: an Epigraph section;
                                  elsewhere a block quote. Ends like verse

![Map of the island](img/map.png "The island, 1921")
                               <- image on a line of its own: alt text, path
                                  (relative to the manuscript; `<…>` or plain,
                                  spaces allowed), optional "caption"; Pandoc
                                  attributes after it size and place it:
                                  `{width=50%}` (rounded to 5, 10–100),
                                  `{.beside}` + `.outside` `.inside` `.left`
                                  `.right`, `{.page}`, `{.bleed}`, combined
                                  as `{.beside .left width=35%}`; others
                                  are ignored

Table: Lydia, my love          <- caption (Pandoc): a `Table: text` line
| Day | Miles |                   alone in its paragraph, right above
|:----|------:|                   the table or after one blank line, or
| 1   | 14    |                   the same below it; shown above, and one
                                  above wins over one below. This is a
                                  pipe table: a header row, a delimiter
                                  row, rows; outer pipes optional, `\|`
                                  is text, cells hold emphasis, links and
                                  notes. The delimiter row sets each
                                  column's alignment (`:--` left, `--:`
                                  right, `:-:` centre, `---` left). The
                                  header row is the header, none when all
                                  of it is empty (`| | |`). A short row
                                  is padded; cells beyond the header's
                                  count are left out, and a table with no
                                  text is dropped: `TableSimplified`.
                                  Merged cells cannot be written here

- Rope, *the long one*,        <- list: `-`, `*` or `+` items, or `1.`/`1)`;
  and the hooks.                  lines joined; after a blank line another
- Matches                         item continues it and an indented line
                                  (2 spaces, tab) is a second paragraph;
  Keep them dry.                  deeper-indented items nest. Starts after
  - in the tin box                a blank line or a block, never inside a
1. Walk to the pier.              paragraph. Ordered: starts at 1, two items
2. Wait for the tide.             at least ("3. Oktober …" is text).
                                  Items counting on from another number
                                  ("8.", "9.") are numbered paragraphs,
                                  with a `ListFlattened` warning

A footnote mark[^1] goes on the word; the definition can be anywhere:

[^1]: Note text, lines joined; after a blank line,
    an indented line (tab or 4 spaces) starts its second paragraph.

Ver&shy;legenheit             <- soft hyphen (or U+00AD itself): the
                                  author's own hyphenation point

<!-- TODO: the year -->        <- HTML comment: never printed, also over
                                  several lines; an unclosed `<!--` is text

***                            <- scene break (also `* * *`, `#`, `~~~`)

\newpage                       <- page break (also `\pagebreak`); dropped at
                                  the start or end of a section

Functions

import

Import a manuscript. The parser does no I/O: files returns the bytes of an image path as written in the manuscript (relative to it), or None if there is no such file. Each path is asked for once. Pass |_| None when no files are at hand; images then warn as missing.