Can HTML IDs Begin with Numbers?

Can IDs Start with Numbers?

In HTML, can elements have IDs initiated or consisting entirely of numbers?

Answer:

Yes, ID values in HTML can consist solely of digits. Characters outside of whitespace are permissible. While earlier HTML versions imposed restrictions on ID values, requiring a specific set of characters and a letter as the starting point, browsers disregarded these limitations. This is reflected in HTML5's specification, which allows greater flexibility.

However, it's worth noting that using IDs starting with numbers can pose challenges when styling elements using CSS selectors. To select an element with an ID starting with a digit, you must escape the character with a backslash. For example, to select an element with ID "12," the CSS selector would be #3132.

Despite these potential drawbacks, you can use numeric IDs in HTML. Here's a demonstration:

<div>
<p>In this example, the background color is set using CSS:</p>
<pre class="brush:php;toolbar:false"># {
    background: #0bf;
}

And the border is set in JavaScript using document.getElementById:

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

Remember that CSS selectors require the ID to be escaped when using numeric IDs. Opting for letter-starting IDs can simplify this process if you intend to use CSS selectors to target elements.