Can HTML IDs Start with a Number?

Can I Have an Element with an ID That Starts with a Number?

Question:

Is it possible to create an element with an ID that begins with or consists entirely of numbers?

Answer:

Yes, it is possible to create an element with an ID that begins with or consists entirely of numbers. However, using CSS selectors to select or style such an element can be challenging.

Explanation:

HTML5 specifications allow for ID values that contain solely digits, as any character except a space is acceptable. While earlier HTML specifications imposed stricter rules, browsers have never strictly enforced them.

ID Selection in CSS:

When using CSS selectors to select elements with numerical IDs, it is important to note the limitations:

• CSS ID selectors cannot directly use IDs that begin with a digit. They must be escaped using backslashes. For example, an ID of "12" would be represented as "#3132".

Best Practice:

For the sake of simplicity, it is recommended to start IDs with a letter if you intend to use CSS selectors to work with them.

Example:

Below is an example that demonstrates the use of a div with the ID "12" and how to interact with it using CSS, JavaScript via document.getElementById, and JavaScript via document.querySelector:

// CSS
# {
  background: #0bf;
}

// JavaScript via getElementById
document.getElementById("12").style.border = "2px solid black";

// JavaScript via querySelector (if supported)
if (document.querySelector) {
  document.querySelector("#\31\32").style.fontStyle = "italic";
}

This example demonstrates that elements with numerical IDs can be manipulated in browsers, but using escaped ID selectors in CSS is necessary to avoid potential conflicts.

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