chore(meta): Document Embedlivesample identifier

[bsmth]

The {{Embedlivesample}} macro currently has two ways of specifying which code blocks to combine into a "result" iframe, and only one of these ways is documented. This PR adds documentation for the "string identifier" method or marking fenced code blocks (HTML/CSS/JS) with an identifier in the info string using:

• ```{language} live-sample___{identifier}

For example, in Markdown, this is used as follows:

## Examples

### Styling a paragraph

In this example, we're using CSS to style paragraphs.

```html live-sample___paragraph-styling
<p>I'm not fancy.</p>
<p class="fancy">But I am!</p>
```

```html
<p>I'm another HTML block. I won't be included in the result.</p>
```

```css live-sample___paragraph-styling
p.fancy {
  color: red;
}
```

Only the `<p>` element with `class="fancy"` will get styled `red`:

{{EmbedLiveSample("paragraph-styling")}}

[github-actions]

Preview URLs

• /en-US/docs/MDN/Writing_guidelines/Page_structures/Code_examples
• /en-US/docs/MDN/Writing_guidelines/Page_structures/Live_samples

External URLs (1)

URL: /en-US/docs/MDN/Writing_guidelines/Page_structures/Code_examples
Title: Code examples

• https://mdn.github.io/learning-area/css/styling-boxes/backgrounds/ (1 time)

(comment last updated: 2023-11-22 09:30:06)

[dipikabh]

Thanks for opening this PR, @bsmth 🙏! I'll take a look now.

[dipikabh]

Thanks, @bsmth. This is good overall. I've added some edit suggestions.

[bsmth]

Thank you for the comments, @dipikabh! 🙏🏻

[bsmth]

Thanks @dipikabh - let's take a look again when you're back.

[dipikabh]

This is looking good, @bsmth. Thanks for the updates.

There's a few suggestions following Vadim's comment about saying "lang ID" vs "class". Leaving a +1 so you can merge after the changes.

[bsmth]

Thanks, both. Going to merge now 🎉