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Glossary of Terms

We have compiled this list of terms and definitions to help you better understand the terminology used within the web development community.

Valid Doctype

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Valid Doctype means your page correctly declares which version of HTML it uses so browsers render it in standards mode. Missing or broken doctypes can trigger quirks mode, causing unpredictable layout and styling problems. It is a simple one-line fix that prevents a surprising number of issues.

Valid Doctype

A valid doctype means your page starts with a properly formatted <!DOCTYPE html> declaration that browsers can recognize and act on. It is the difference between your browser saying "great, I will use modern rendering rules" and "I have no idea what this is, so I will guess." A valid doctype keeps rendering predictable and consistent across every browser.

Why It Matters

  • Invalid doctypes trigger quirks mode. A malformed or unrecognized doctype is treated the same as no doctype at all. The browser falls into quirks mode, applying unpredictable legacy rendering rules.
  • Validation catches errors early. When your doctype is valid, HTML validators can check the rest of your page against the correct specification. An invalid doctype undermines the entire validation process.
  • It ensures CSS consistency. Properties like box-sizing, percentage widths on tables, and inline element spacing all behave differently in quirks mode. A valid doctype ensures your CSS works the way you wrote it.
  • It is the simplest thing to get right. The modern HTML5 doctype is just 15 characters: <!DOCTYPE html>. There is no excuse for getting it wrong when the correct version is this straightforward.

How to Ensure a Valid Doctype

  1. Use the standard HTML5 declaration. <!DOCTYPE html> is all you need. It works for all HTML5 pages and is backwards compatible with older content.
  2. Place it on the very first line. The doctype must be the absolute first thing in the document. No whitespace, no comments, no server-side output before it.
  3. Check for typos. A missing exclamation point, extra spaces, or misspelling can make the doctype invalid. <!DOCTYPE html> — exactly like that.
  4. Validate your pages. Use an HTML validator to confirm your doctype is recognized. Valid pages start with a valid doctype declaration — it is the first thing the validator checks.
  5. Audit CMS templates and includes. Server-side includes, template engines, and CMS themes sometimes output content before the doctype. Check the actual rendered source, not just the template file.

Common Mistakes

  • Misspelling the doctype. <!DOCKTYPE html> or <!doctyp html> will not be recognized. Browsers are surprisingly strict about this particular string.
  • Using old XHTML or HTML 4 doctypes verbatim. Long-form doctypes from earlier HTML versions still technically work, but there is no reason to use them. Switch to the short HTML5 version.
  • Server output before the doctype. PHP warnings, BOM characters, or stray whitespace echoed before the HTML starts can push the doctype out of position, triggering quirks mode.
  • Assuming it does not matter anymore. Even though HTML5 simplified the doctype, it is still required. Browsers still check it. Omitting it still has consequences.
Bottom Line: Make sure every page starts with a correctly spelled <!DOCTYPE html> on the very first line. It is 15 characters that tell the browser to behave properly — skip it and you are asking for layout surprises.
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Synonyms: DOCTYPE Declaration, Standards Mode

What Does "Liquid Purple" mean?

noun | / LIK-wid PUR-pul /

  1. (biochemistry) Also known as visual purple or rhodopsin — a light-sensitive receptor protein found in the rods of the retina. It enables vision in dim light by transforming invisible darkness into visible form. Derived from the Greek rhódon (rose) and ópsis (sight), its name reflects its delicate pink hue and vital role in perception.

  2. (modern usage) Liquid Purple — a digital marketing agency specializing in uncovering unseen opportunities and illuminating brands hidden in the digital dark. Much like its biological namesake, Liquid Purple transforms faint signals into clear visibility — revealing what others overlook and bringing businesses into the light.

Origin: From the scientific term rhodopsin, discovered by Franz Christian Boll in 1876; adopted metaphorically by a marketing firm dedicated to visual clarity in the age of algorithms.

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For over 20 years, Liquid Purple has been headquartered in the heart of Southern California, serving clients across Irvine, Newport Beach, Anaheim, and the greater Los Angeles area. While we are proud of our local roots, our digital reach extends far beyond our local area. We support businesses in major hubs like Denver, Dallas, New York, and Miami, as well as international clients. Our ability to operate across time zones means you can often wake up to completed tasks and progress updates—keeping your business moving while you sleep.