Add contentLevel Lua option and a \markinline plain TeX command

[Witiko]

Currently, we only support including whole Markdown documents using the \markdownInput and \markdownBegin ... End commands. However, it would be useful to allow including just inline elements using a command \markinline with a syntax similar to \mintinline from the minted package:

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Hello, \markinline{*world*} !

Expected output: Hello, world !

---

In LaTeX, the command would also support optional arguments similar to the \markdownInput command and the \begin{markdown} enviroment (see #299).

At the level of Lua, we would add a new option contentLevel, which could have two values: block or inline. The default value would be inline for the \markinline command and block in general. For contentLevel of inline, only a series of inline level elements would be allowed in reader->convert(). For contentLevel of block, the behavior would be the same as it is now.

Tasks

• Add contentType Lua option.
• Add plain TeX command \markinline.

[Witiko]

Here are some thoughts regarding the \markinline command:

1. It would be neat if we could support "braceless" invocation, i.e. if users could write not only \markinline{*Hello, world!*} and \markinline"*Hello, world!*" but also \markinline *Hello, world!*. This would allow users to shorthand \markinline to e.g. \m and type markdown in TeX with little visual noise. On the technical side of things, TeX would likely not distinguish * from " and stripping " / not stripping * would happen in Lua. The approach should be extensible, i.e. \markinline ~~deleted text~~ should produce "deleted text" when strikeThrough is enabled and "~deleted text~" otherwise.

   We should be able to do this by converting the original text and seeing if the initial and final characters from the input are still present in the output. If they are, they do not surround an element, so we strip them and repeat the conversion. Otherwise, we return the result of the conversion. To maintain correctness, we should only do this when we use \markinline without {}, i.e. when the text starts and ends with the same character and a new internal option _stripDelimiters is enabled. To prevent repeated conversion when users don't use braceless invocation speed, we should only do this when the surrounding characters are special characters.

2. Currently, all buffering commands all produce a temporary file with the markdown text that is then processed by \markdownInput. While this is conceptually simple, it requires the creation of a needless temporary file in LuaTeX. In the next major release, we should decouple \markinline and \markdownReadAndConvert from \markdownInput, buffer the text in a token list and have LuaTeX access that token list directly.