3 ms·

I believe xhtml made uppercase tags invalid.

• officemonkey 11y ago
  That is correct. From "XHTML™ 1.0 The Extensible HyperText Markup Language (Second Edition)" 4.2. Element and attribute names must be in lower case XHTML documents must use lower case for all HTML element and attribute names. This difference is necessary because XML is case-sensitive e.g. <li> and <LI> are different tags.