Hi all,

Some food for thought on simple code block namespaces.

Re: https://github.com/github/markup/issues/533

I’m the main author of KeenWrite (see screenshots 
<https://github.com/DaveJarvis/keenwrite/blob/master/docs/screenshots.md>), 
a type of desktop Markdown editor that supports diagrams. It’s encouraging 
to see that Mermaid diagrams are being supported in GitHub. There are a few 
drawbacks on the syntax and implications of using MermaidJS.

First, only browser-based SVG renderers can correctly parse Mermaid 
diagrams. I’ve tested Apache Batik, svgSalamander, resvg, rsvg-convert, 
svglib, CairoSVG, ConTeXt, and QtSVG. See issue 2485 
<https://github.com/mermaid-js/mermaid/issues/2485>. This implies that 
typesetting Mermaid documents is not currently possible. In effect, by 
including Mermaid diagrams, many documents will be restricted to web-based 
output, excluding the possibility of producing PDF documents based on 
GitHub markdown documents (for the foreseeable future).

Second, there are numerous text-to-diagram facilities available beyond 
Mermaid. The server at https://kroki.io/ supports Mermaid, PlantUML, 
Graphviz, byte fields, and many more. While including MermaidJS is a great 
step forward, supporting Kroki diagrams would allow a much greater variety. 
(Most diagrams produced in MermaidJS can also be crafted in Graphviz, 
albeit with less terse syntax.)

Third, see the CommonMark discussion thread 
<https://talk.commonmark.org/t/mermaid-generation-of-diagrams-and-flowcharts-from-text-in-a-similar-manner-as-markdown/1882> 
referring to a syntax for diagrams. It’s unfortunate that a standard 
“namespace” concept was not proposed.

Fourth, KeenWrite integrates Kroki. To do so, it uses a variation on the 
syntax:

``` diagram-mermaid
```

``` diagram-graphviz
```

``` diagram-plantuml
```

The diagram- prefix tells KeenWrite that the content is a diagram. The 
prefix is necessary to allow using *any* diagram supported by a Kroki 
server without having to hard-code the supported diagram type within 
KeenWrite. Otherwise, there is no simple way to allow a user to mark up a 
code block with their own text style that may coincide with an existing 
diagram type name.

Fifth, if ever someone wants to invent a programming language named Mermaid 
(see MeLa 
<https://pdfs.semanticscholar.org/7d75/49b737fd1d85bdaee016681e8915fea81ad9.pdf>), 
then it precludes the possibility of using the following *de facto* syntax 
highlighting:

``` mermaid
```

My feature request is to add support for Kroki and the diagram- prefix 
syntax. That is:

``` diagram-mermaid
```

And deprecate the following syntax:

``` mermaid
```

And, later, introduce the language- prefix for defining code blocks that 
highlight syntax. That is, further deprecate:

``` java
```

With the following:

``` language-java
```

That would provide a “namespace” of sorts to avoid naming conflicts in the 
future.

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