HTML/CSS Case Sensitivity

By Xah Lee. Date: . Last updated: .

Case sensitivity:

HTML tag names
Case insensitive. <div> = <DIV>
HTML attribute name
Case insensitive. class= = CLASS=.
HTML attribute values
Case sensitive. class="aaa" ≠ class="AAA".
XML tag name
Case sensitive. Must be lowercase.
XML attribute name
Case sensitive. class= ≠ CLASS=
XML attribute values
Case sensitive. class="aaa" ≠ class="AAA".
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.aaa ≠ div.AAA

Allowed Characters and Case Sensitivity