What values are valid for an ID attribute in an HTML element?

When naming id attributes of HTML tags, you do have some limits.

As stated by the HTML4 specification...

>> ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").

Source: https://www.w3.org/TR/html4/types.html#type-id

HTML5 has more-relaxed specifications...

There are no other restrictions on what form an ID can take; in particular, IDs can consist of just digits, start with a digit, start with an underscore, consist of just punctuation, etc.

Source: https://www.w3.org/TR/html5/dom.html#element-attrdef-global-id

How to Wrap Text in Pre-Tags in HTML

You can use PRE tags to make text look like code in most computer terminals, which is a monospaced, Courier font.

But the problem with PRE tags is that the text does not wrap automatically. If the user wants to see a long paragraph, they need to scroll RIGHT on their computer screen, instead of DOWN, which is more intuitive.

To make PRE tagged text autowrap, the code is very simple...

pre {
white-space: pre-wrap;
}

All PRE-tags are now wrapped. This solution will work on all modern browsers.

If you want a solution that works on older machines, the code is a bit more complex...

pre {
white-space: pre-wrap; /* css-3 */
white-space: -moz-pre-wrap; /* Mozilla, since 1999 */
white-space: -pre-wrap; /* Opera 4-6 */
white-space: -o-pre-wrap; /* Opera 7 */
word-wrap: break-word; /* Internet Explorer 5.5+ */
}

(Multi-Browser Solution Source: https://longren.io/wrapping-text-inside-pre-tags/ )