Case Sensitivity in {HTML5, XML, CSS, JavaScript}

By Xah Lee. Date: . Last updated: .

{HTML4, HTML5} → No

HTML4, HTML5: tag names are NOT case sensitive. You can write <P cLAss="…">…</p>.

{XHTML, XML} → Yes

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

Attribute Values → Yes

Attribute values (e.g. id="…", class="…"), 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

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