Can I BEGIN a CSS selector ID or Class with an underscore? [duplicate]

Question

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Which characters are valid in CSS class names/selectors? (11 answers)

Closed 9 years ago.

For example: #_id-name {} and ._class-name {} I know that in the early days underscores were not allowed at all - as well as double hyphens (--). But is it OK and would all browsers be able to read/understand a class or an ID if it starts with an _?

Answer 1

I'm basing my answer on html rather than just CSS. Documentation:

• http://www.w3.org/TR/html401/struct/global.html#h-7.5.2
• ID or NAME
• CDATA (classes)

To summarize, the id must apparently begin with a letter (A-Za-z) and can have any other letters, numbers, underscore, or dash after that. Practically, you can start the id with - or _ and it will work: http://jsfiddle.net/ExplosionPIlls/y6jvs/ but starting with a number does not work.

While these restrictions don't appear to apply to classes which are a CDATA list, practically it seems to work the same: http://jsfiddle.net/ExplosionPIlls/y6jvs/1/

So you get a consistent and future proof browser experience, I would try to avoid doing anything funky with IDs, class names, etc.