Add additional documentation for code highlighting

Author: matalo33

exampleSite/content/cont/markdown.en.md

@@ -164,7 +164,7 @@ and this HTML:
 <em>rendered as italicized text</em>
 ```
 
-### strikethrough
+### Strikethrough
 
 In GFM (GitHub flavored Markdown) you can do strikethroughs.
 
@@ -420,7 +420,7 @@ HTML:
 
 Use "fences"  ```` ``` ```` to block in multiple lines of code.
 
-```markup
+```markdown
 Sample text here...
 ```
 
@@ -434,9 +434,13 @@ HTML:
 
 ### Syntax highlighting
 
-GFM, or "GitHub Flavored Markdown" also supports syntax highlighting. To activate it, simply add the file extension of the language you want to use directly after the first code "fence", ` ```js `, and syntax highlighting will automatically be applied in the rendered HTML. For example, to apply syntax highlighting to JavaScript code:
+GFM, or "GitHub Flavored Markdown" also supports syntax highlighting. To activate it, simply add the file extension of the language you want to use directly after the first code "fence", ` ```js `, and syntax highlighting will automatically be applied in the rendered HTML.
 
-<!-- markdownlint-disable MD046 -->
+See [Code Highlighting]({{< ref "syntaxhighlight.md" >}}) for additional documentation.
+
+For example, to apply syntax highlighting to JavaScript code:
+
+```plaintext
     ```js
     grunt.initConfig({
       assemble: {
@@ -457,7 +461,7 @@ GFM, or "GitHub Flavored Markdown" also supports syntax highlighting. To activat
       }
     };
     ```
-<!-- markdownlint-disable MD046 -->
+```
 
 Renders to:
 

exampleSite/content/cont/syntaxhighlight.en.md

@@ -0,0 +1,89 @@
+---
+date: 2020-06-01T13:31:12+01:00
+title: Code highlighting
+weight: 16
+---
+
+Learn theme uses [highlight.js](https://highlightjs.org/) to provide code syntax highlighting.
+
+## Markdown syntax
+
+Wrap the code block with three backticks and the name of the language. Highlight will try to auto detect the language if one is not provided.
+
+<!-- markdownlint-disable MD046 -->
+```plaintext
+    ```json
+    [
+      {
+        "title": "apples",
+        "count": [12000, 20000],
+        "description": {"text": "...", "sensitive": false}
+      },
+      {
+        "title": "oranges",
+        "count": [17500, null],
+        "description": {"text": "...", "sensitive": false}
+      }
+    ]
+    ```
+```
+<!-- markdownlint-disable MD046 -->
+
+Renders to:
+
+```json
+[
+  {
+    "title": "apples",
+    "count": [12000, 20000],
+    "description": {"text": "...", "sensitive": false}
+  },
+  {
+    "title": "oranges",
+    "count": [17500, null],
+    "description": {"text": "...", "sensitive": false}
+  }
+]
+```
+
+## Supported languages
+
+Learn theme ships with its own version of highlight.js to support offline browsing. The included package supports 38 common languages, as described on the [highlight.js download page](https://highlightjs.org/download/).
+
+## Identifying failed language detection
+
+Highlight will write a warning to the browser console if a requested language was not found. For example, the following code block references an imaginary language `foo`. An error will be output to the console on this page.
+
+```plaintext
+    ```foo
+    bar
+    ```
+```
+
+```nohighlight
+Could not find the language 'foo', did you forget to load/include a language module?(anonymous) @ highlight.pack.js
+```
+
+## Supporting additional languages
+
+To support languages other than the 38 common languages included in the default highlight.js you will need to download your own version of highlight.js and add it to your site content.
+
+### Download custom highlight.js
+
+Visit [https://highlightjs.org/download/](https://highlightjs.org/download/) and select your desired language support. Note that more languages means greater package size.
+
+### Add custom highlight.js to static resources
+
+Inside the zip archive downloaded from highlight.js extract the file named `highlight.pack.js`. Move this file to the **new** location
+
+```nohighlight
+static/js/highlight.pack.js
+```
+
+**Do not** replace the existing file at `themes/hugo-theme-learn/static/js/highlight.pack.js`.
+
+Including the file in the correct path will override the theme default highlight.pack.js and prevent issues caused in the future if the theme default file is updated.
+
+## Further usage information
+
+See [https://highlightjs.org/usage/](https://highlightjs.org/usage/)