docs: use only fenced code blocks (#16044)

.markdownlint.yml

@@ -15,4 +15,5 @@ MD029: false     # Ordered list item prefix
 MD030: false     # Spaces after list markers
 MD033: false     # Allow inline HTML
 MD041: false     # First line in file should be a top level header
-MD046: false     # Code block style
+MD046:           # Code block style
+    style: fenced

docs/src/developer-guide/development-environment.md

@@ -47,11 +47,15 @@ Now, the remote `upstream` points to the upstream source.
 
 [Yeoman](http://yeoman.io) is a scaffold generator that ESLint uses to help streamline development of new rules. If you don't already have Yeoman installed, you can install it via npm:
 
-    npm install -g yo
+```shell
+npm install -g yo
+```
 
 Then, you can install the ESLint Yeoman generator:
 
-    npm install -g generator-eslint
+```shell
+npm install -g generator-eslint
+```
 
 Please see the [generator documentation](https://github.com/eslint/generator-eslint) for instructions on how to use it.
 

docs/src/developer-guide/source-code.md

@@ -14,7 +14,9 @@ ESLint is hosted at [GitHub](https://github.com/eslint/eslint) and uses [Git](ht
 
 If you simply want to create a local copy of the source to play with, you can clone the main repository using this command:
 
-    git clone git://github.com/eslint/eslint.git
+```shell
+git clone git://github.com/eslint/eslint.git
+```
 
 If you're planning on contributing to ESLint, then it's a good idea to fork the repository. You can find instructions for forking a repository at [https://help.github.com/articles/fork-a-repo/](https://help.github.com/articles/fork-a-repo/). After forking the ESLint repository, you'll want to create a local copy of your fork.
 
@@ -27,8 +29,10 @@ Before you can get started developing, you'll need to have a couple of things in
 
 Once you have a local copy and have Node.JS and npm installed, you'll need to install the ESLint dependencies:
 
-    cd eslint
-    npm install
+```shell
+cd eslint
+npm install
+```
 
 Now when you run `eslint`, it will be running your local copy and showing your changes.
 

docs/src/developer-guide/unit-tests.md

@@ -14,15 +14,19 @@ Most parts of ESLint have unit tests associated with them. Unit tests are writte
 
 When you first get the source code, you need to run `npm install` once initially to set ESLint for development. Once you've done that, you can run the tests via:
 
-    npm test
+```shell
+npm test
+```
 
 This automatically starts Mocha and runs all tests in the `tests` directory. You need only add yours and it will automatically be picked up when running tests.
 
 ## Running Individual Tests
 
 If you want to quickly run just one test file, you can do so by running Mocha directly and passing in the filename. For example:
 
-    npm run test:cli tests/lib/rules/no-undef.js
+```shell
+npm run test:cli tests/lib/rules/no-undef.js
+```
 
 If you want to run just one or a subset of `RuleTester` test cases, add `only: true` to each test case or wrap the test case in `RuleTester.only(...)` to add it automatically:
 
@@ -50,4 +54,6 @@ Running individual tests is useful when you're working on a specific bug and ite
 
 The default timeout for tests in `npm test` is 10000ms. You may change the timeout by providing `ESLINT_MOCHA_TIMEOUT` environment variable, for example:
 
-    ESLINT_MOCHA_TIMEOUT=20000 npm test
+```shell
+ESLINT_MOCHA_TIMEOUT=20000 npm test
+```

docs/src/pages/rules.md

@@ -84,3 +84,5 @@ Rules in ESLint are grouped by type to help you understand their purpose. Each r
     }) }}
 {%- endfor -%}
 {%- endif -%}
+
+{# <!-- markdownlint-disable-file MD046 --> #}

docs/src/rules/no-irregular-whitespace.md

@@ -32,30 +32,32 @@ This rule is aimed at catching invalid whitespace that is not a normal tab and s
 
 This rule disallows the following characters except where the options allow:
 
-    \u000B - Line Tabulation (\v) - <VT>
-    \u000C - Form Feed (\f) - <FF>
-    \u00A0 - No-Break Space - <NBSP>
-    \u0085 - Next Line
-    \u1680 - Ogham Space Mark
-    \u180E - Mongolian Vowel Separator - <MVS>
-    \ufeff - Zero Width No-Break Space - <BOM>
-    \u2000 - En Quad
-    \u2001 - Em Quad
-    \u2002 - En Space - <ENSP>
-    \u2003 - Em Space - <EMSP>
-    \u2004 - Three-Per-Em
-    \u2005 - Four-Per-Em
-    \u2006 - Six-Per-Em
-    \u2007 - Figure Space
-    \u2008 - Punctuation Space - <PUNCSP>
-    \u2009 - Thin Space
-    \u200A - Hair Space
-    \u200B - Zero Width Space - <ZWSP>
-    \u2028 - Line Separator
-    \u2029 - Paragraph Separator
-    \u202F - Narrow No-Break Space
-    \u205f - Medium Mathematical Space
-    \u3000 - Ideographic Space
+```text
+\u000B - Line Tabulation (\v) - <VT>
+\u000C - Form Feed (\f) - <FF>
+\u00A0 - No-Break Space - <NBSP>
+\u0085 - Next Line
+\u1680 - Ogham Space Mark
+\u180E - Mongolian Vowel Separator - <MVS>
+\ufeff - Zero Width No-Break Space - <BOM>
+\u2000 - En Quad
+\u2001 - Em Quad
+\u2002 - En Space - <ENSP>
+\u2003 - Em Space - <EMSP>
+\u2004 - Three-Per-Em
+\u2005 - Four-Per-Em
+\u2006 - Six-Per-Em
+\u2007 - Figure Space
+\u2008 - Punctuation Space - <PUNCSP>
+\u2009 - Thin Space
+\u200A - Hair Space
+\u200B - Zero Width Space - <ZWSP>
+\u2028 - Line Separator
+\u2029 - Paragraph Separator
+\u202F - Narrow No-Break Space
+\u205f - Medium Mathematical Space
+\u3000 - Ideographic Space
+```
 
 ## Options