## Validation Error: Invalid Character

### Error: The invalid character X is used in selector XXX

The selector indicated contains an invalid character. Selectors should contain only letters, numbers, periods (. for classes), and pound signs (# for IDs). Do not use other special characters or spaces.

Note: Using underscores in class names is a common cause of cross-browser headaches. While some browsers support the use of underscores, others (such as Netscape 4.x) do not. For this reason, you should avoid using undercores in selectors.

Related topics: Configuring the Style Checker, CSS Structure and Rules

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