HTML/CSS Case Sensitivity

By Xah Lee. Date: 2012-03-29. Last updated: 2021-05-13.

Case sensitivity:

HTML tag names: Case insensitive. <div> = <Div>
HTML attribute name: Case insensitive. class= = Class=.
HTML attribute values: Case sensitive. class="A" ≠ class="a".
XML/XHTML tag name: Case sensitive. Must be lowercase.
XML/XHTML attribute name: Case sensitive. class= ≠ Class=
XML/XHTML attribute values: Case sensitive. class="A" ≠ class="a".
CSS selectors for html tag names: Case insensitive. div.x = Div.x
CSS selectors for html attribute names: Case insensitive. div[target] = div[TARget]
CSS selectors for html attribute values: Case sensitive. div.a ≠ div.A