HTML - Browser parsing rules and invalid HTML handling

What it actually means

Browsers do not fail on invalid HTML. They auto-correct it using predefined parsing rules. This silent correction often causes unexpected layout and behavior issues.

How to use it correctly

Examples of invalid structures:

<p>
  <div>Text</div>
</p>

What the browser actually does:

  • Closes <p> automatically

  • Moves <div> outside

Another common issue:

<ul>
  <div>Item</div>
</ul>

Only <li> is allowed inside <ul>.

Why this matters

  • Layout breaks without visible errors

  • CSS behaves unpredictably

  • JavaScript selectors fail

  • Debugging becomes difficult

Browsers fixing your HTML does not mean your HTML is correct.

Accessibility impact

  • Screen readers follow the corrected DOM, not your source code

  • Reading order may change silently

  • Landmarks may be lost

Practical rule

Always validate HTML.
If the DOM structure surprises you, check for invalid nesting first.