Case Sensitivity of HTML5, XML, CSS, JavaScript

By Xah Lee. Date: . Last updated: .

{HTML4, HTML5} → No

HTML4, HTML5: tag names and attribute names are NOT case sensitive. You can write <DIV cLAss="…">…</div>.

{XHTML, XML} → Yes

XHTML, XML: case sensitive, and must be all lowercase.

Attribute Values → Yes

Attribute values (example: id="value", class="value"), in HTML and XML are case sensitive.


JavaScript → Yes

JavaScript identifier (variable and function name) is case sensitive. [see JavaScript Basics]

Allowed Characters in Attribute Names

HTML: Allowed Characters in id Attribute

Allowed Characters in JavaScript Identifiers

JS: Allowed Characters in Identifier

HTML Basics

  1. HTML Basics
  2. HTML5 Tags
  3. Case Sensitivity
  4. Allowed Characters
  5. Charset and Encoding
  6. Self-Closing Tags
  7. Multiple Class Value
  8. HTML Entity List

HTML Table

  1. HTML Table Examples
  2. HTML Table, thead, tbody, tfoot
  3. HTML Table, colgroup, col
  4. Styling HTML Table with CSS
  5. CSS: 3 Columns Page Layout
  6. Pure CSS Table


  1. Viewport Meta
  2. the Root Element
  3. iframe
  4. video
  5. audio
  6. figure
  7. dl, dt, dd
  8. s strike del
  9. time
  10. meter
  11. progress
  12. q
  13. address
  14. canvas
  15. ruby
  16. HTML5 Custom Data Attribute
  17. Big Tag
  18. Image Maps
  19. Marquee, Scrolling Text
  20. How to Markup Subtitle
  21. Meta Language Tag Obsolete
  22. Browser Auto Refresh

HTML4 Frameset

  1. HTML: Split Windows; Frameset
  2. HTML Nested Frameset
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