What's the difference between HTML and XHTML?

  • XHTML elements must be properly nested.
  • XHTML elements must always be closed.
  • XHTML elements must be in lowercase.
  • XHTML documents must have one root element.
  • XHTML DOCTYPE is mandatory.

What is the use of data-* attribute?

Use the data-* attribute to embed custom data. The data-* attributes is used to store custom data private to the page or application. The data-* attributes gives us the ability to embed custom data attributes on all HTML elements.

What's the difference between standards mode and quirks mode?

The almost standards mode is also known as the limited quirks mode. As you can imagine, the content rendered in the almost standards mode is almost fully compliant with the full standards mode. The almost standards mode renders the document with only a few quirks that have to do with the vertical sizing of table cells.