To Quote or Not to Quote: When Are Quotes Necessary in CSS Attribute Selectors?

Using Quotes in CSS Attribute Selectors: The Definitive Guide

When working with CSS attribute selectors, you've probably faced the dilemma of using quotes or not. This article delves into the rules and provides clarity on this topic.

The CSS specification states that attribute values in CSS selectors can be enclosed in single or double quotes or omitted altogether. However, it's essential to understand the exceptions:

1. Required Quotes:

   • Attribute values containing spaces must be enclosed in quotes.
   • Attribute values starting with a digit must be quoted.
   • Attribute values containing special characters (e.g., <, >, &, ', ") must be quoted.

2. Optional Quotes:

   • Alphanumeric attribute values with no spaces or special characters can be omitted without quotes.
   • You can also include quotes around such values for consistency and clarity.

3. Invalid:

   • Using both single and double quotes around the same attribute value is invalid.
   • Using quotes for attribute values that contain only numbers (without leading zeros) is invalid.

To simplify the process, consider referencing the Unquoted Attribute Value Validator tool at http://mothereff.in/unquoted-attributes. It will help you determine whether quotes are necessary for your attribute values.

As a general rule, it's good practice to use quotes even for optional attribute values, ensuring valid markup and avoiding potential issues.

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