Forms and validation · Lesson 6 of 10 · 7 minutes

Forms and validation: Error messages

An error needs both a specific explanation and a programmatic relationship to the invalid control.

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Your objectives

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1
Build error messages
Build this first target: <label> (for="email") containing “Email”; <input> (id="email", type="email"). Inspect the structure before checking the lesson.
Hint & worked example
An error needs both a specific explanation and a programmatic relationship to the invalid control.
The requested elements, attributes, content, and hierarchy exist outside comments.
```
<label for="email">Email</label><input id="email" type="email">
```
Common mistake to avoid: A visual appearance alone guarantees the intended HTML meaning.
2
Extend the error messages example
Extend your file to include: <label> (for="email") containing “Email”; <input> (id="email", type="email", aria-invalid="true"); <p> (id="email-error") containing “Enter an address including @.”. Inspect the structure before checking the lesson.
Hint & worked example
An error needs both a specific explanation and a programmatic relationship to the invalid control.
The requested elements, attributes, content, and hierarchy exist outside comments.
```
<label for="email">Email</label><input id="email" type="email" aria-invalid="true"><p id="email-error">Enter an address including @.</p>
```
Common mistake to avoid: Replacing semantic elements with generic divs automatically improves accessibility.
3
Verify the complete error messages pattern
Finish the pattern with: <label> (for="email") containing “Email”; <input> (id="email", type="email", aria-invalid="true", aria-describedby="email-error"); <p> (id="email-error") containing “Enter an address including @.”. Inspect the structure before checking the lesson.
Hint & worked example
An error needs both a specific explanation and a programmatic relationship to the invalid control.
The requested elements, attributes, content, and hierarchy exist outside comments.
```
<label for="email">Email</label><input id="email" type="email" aria-invalid="true" aria-describedby="email-error"><p id="email-error">Enter an address including @.</p>
```
Common mistake to avoid: A visual appearance alone guarantees the intended HTML meaning.

Understand the pattern

An error needs both a specific explanation and a programmatic relationship to the invalid control.

Misconceptions to reject

A visual appearance alone guarantees the intended HTML meaning.
Replacing semantic elements with generic divs automatically improves accessibility.

The preview is a sanitized subset, not a full browser compatibility test.

Worked example and expected result

<label for="email">Email</label><input id="email" type="email" aria-invalid="true" aria-describedby="email-error"><p id="email-error">Enter an address including @.</p>

An error needs both a specific explanation and a programmatic relationship to the invalid control.

Try a variation

Adapt the final example to a different project name while retaining its structure and relationships. A different context still needs a real browser and accessibility check.

Explain it

Which statement correctly explains error messages?A visual appearance alone guarantees the intended HTML meaning.Replacing semantic elements with generic divs automatically improves accessibility.An error needs both a specific explanation and a programmatic relationship to the invalid control.

Apply it elsewhere

You reuse error messages in a different project. What must still be verified?Only whether the source code has the same number of lines.The meaning, relationships, and accessible names in the new document.Nothing; passing a single exercise guarantees every future use.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Forms and validation: Input descriptions Try an incident drill

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MDN: HTML structure