Added support for plaintext

[RunDevelopment]

This came up in #2665:

Right now, we use language-none (or just none) to mean "no language" but that has actually two meanings. "No language" could mean either plaintext or that the language is undefined/unknown. These two distinct concepts are both represented by none.

This is a problem when language detection comes into play. A code block with no (defined) language will get language none by default, so the language detector can do its job. But what happens for a plaintext code block? The user will use the language-none class to indicate plaintext. But these two cases are indistinguishable from the perspective of the language detector.

The simple solution for this problem is to split none into two languages: none and plain.
From now on, none only represents an undefined/unknown language and plain will represent plaintext.

This solves the problem has some additional advantages as well. Since none has no grammar, plugins like Show Invisibles cannot be used. plain will have an empty grammar, so plugins like SI will work.

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I'm also thinking about giving plain some aliases like plaintext, plain-text, text, and txt but this will make the implementation less simple.

[github-actions]

JS File Size Changes (gzipped)

A total of 2 files have changed, with a combined diff of +27 B (+0.5%).

file	master	pull	size diff	% diff
components/prism-core.min.js	3.03 KB	3.04 KB	+15 B	+0.5%
plugins/show-language/prism-show-language.min.js	2.27 KB	2.28 KB	+12 B	+0.5%

Generated by 🚫 dangerJS against b6ad5d7

[joshgoebel]

I'm also thinking about giving plain some aliases like plaintext, plain-text, text, and txt but this will make the implementation less simple.

Just FYI in Highlight.js we named the grammar 'plaintext' and have aliases for txt and text.

[RunDevelopment]

I'm also thinking about giving plain some aliases like plaintext, plain-text, text, and txt but this will make the implementation less simple.

Just FYI in Highlight.js we named the grammar 'plaintext' and have aliases for txt and text.

Thanks for the info! In that case, I'll add the aliases.