Why Use Backslashes in CSS Class Names Like \'.container.\\31 25\\25\'?

What's the Purpose of the Backslash Character in CSS's ".container.31 2525"?

In the provided CSS code, the backslash character () serves a specific purpose related to identifier escaping. According to the CSS specification:

• Escaping Special Characters: A backslash can cancel the meaning of special CSS characters. In this case, it prevents the percentage sign (%) from being recognized as the start of a CSS calculation.
• Numeric Code Point References: When followed by six hexadecimal digits, a backslash can represent a specific Unicode character. This allows authors to refer to characters that are not easily entered in the document.

In the example:

.container.31 2525 is equivalent to .container[class ~= "125%"].

• 31 is the hexadecimal representation of the number 1.
• 25 is the hexadecimal representation of the number 17.
• 25 is the percent sign, escaped to remove its special meaning.

Therefore, the backslash escapes the percentage sign, allowing it to be treated as part of the identifier rather than a calculation. This technique ensures that the "125%" value is interpreted as a class name rather than a calculation.

Without the backslash, the identifier would start with a number and be invalid as per CSS syntax:

• .container.125% is invalid because identifiers cannot start with a number.

By using the backslash, the percentage values can be used as class names, enabling flexible styling based on container sizes.

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