Comments and processing instructions

Last reviewed May 28, 2026 Content v20260528

Track mode

iframe_xml

Means

XML preview sandbox

Reading

~1 min

Level

beginner

This lesson

This lesson teaches Comments and processing instructions—the ideas, syntax, and habits you need before moving on in XML.

Without a solid grasp of Comments and processing instructions, you will repeat mistakes in XML exercises and on real pages or scripts.

You will apply Comments and processing instructions in contexts like: Enterprise integration, publishing pipelines, Android resources, and data exchange alongside JSON.

Edit XML in the playground, watch well-formedness feedback, preview rendered output, then complete the quizzes.

When the previous lesson's MCQs feel easy and you can explain Comments and processing instructions in your own words.

Comments:  — not nested. Processing instructions pass hints to apps: <?xml-stylesheet href="x.css"?>

Going deeper

In production XML work, Comments and processing instructions matters when documents, stylesheets, or apps must stay maintainable across teams and releases—not only in isolated demos.

Common pitfalls

Watch for copy-paste configs, skipping validation or tests, and mixing concerns (structure vs presentation vs behavior) in one layer.

Practice

Apply one technique from this lesson in the playground.
Write one interview-style sentence explaining when you would use comments and processing instructions on a real project.

Playground

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Discussion

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Starter discussion topics

What part of this lesson needs a second read?
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