🏗️Document Structure
<!DOCTYPE html>HTML5 document declaration
<html lang='en'>Root element with language
<head>...</head>Metadata container
<meta charset='UTF-8'>Character encoding
<meta name='viewport'>Responsive viewport tag
<title>Browser tab title
<body>Visible page content
📝Text & Headings
<h1> – <h6>Headings (1=largest)
<p>Paragraph
<strong>Bold (semantic importance)
<em>Italic (emphasis)
<small>Fine print / secondary text
<mark>Highlighted text
<del> / <ins>Deleted / inserted text
<abbr title='...'>Abbreviation with tooltip
<code>Inline code snippet
<pre>Preformatted block
<blockquote>Long quotation
<cite>Reference/citation
🔗Links & Media
<a href='url'>Hyperlink
target='_blank'Open in new tab
rel='noopener noreferrer'Security for _blank links
<img src='' alt=''>Image (always use alt!)
<picture>Responsive image container
<source srcset=''>Multiple image sources
<video controls>Video player
<audio controls>Audio player
<iframe src=''>Embed external content
loading='lazy'Lazy-load images/iframes
📋Lists
<ul>Unordered (bullet) list
<ol>Ordered (numbered) list
<li>List item
<dl> / <dt> / <dd>Description list / term / detail
start='5'Start ordered list at 5
reversedReverse order numbering
type='A'Alphabetical list type
📝Forms
<form action='' method=''>Form container
<input type='text'>Text input
<input type='email'>Email input (validates)
<input type='password'>Password field
<input type='checkbox'>Checkbox
<input type='radio'>Radio button
<input type='file'>File upload
<textarea>Multi-line text
<select> / <option>Dropdown select
<button type='submit'>Submit button
required / disabledValidation attributes
placeholder='...'Input hint text
autocomplete='off'Disable autocomplete
🧱Semantic HTML5
<header>Page/section header
<nav>Navigation links
<main>Primary content (once per page)
<article>Self-contained content
<section>Thematic grouping
<aside>Sidebar / supplementary
<footer>Page/section footer
<figure> / <figcaption>Image with caption
<details> / <summary>Expandable disclosure
<dialog>Modal dialog element
<template>Inert content template
<slot>Web component slot
📊Tables
<table>Table container
<thead> / <tbody> / <tfoot>Table sections
<tr>Table row
<th scope='col'>Header cell (accessible)
<td>Data cell
colspan / rowspanMerge cells
<caption>Table caption/title
🔍Meta & SEO Tags
<meta name='description'>Page description (SEO)
<meta name='robots'>Crawler instructions
<link rel='canonical'>Canonical URL
og:title / og:imageOpen Graph meta tags
twitter:cardTwitter card type
<link rel='icon'>Favicon link
<link rel='preconnect'>Preconnect to domain
<script defer>Load JS after parsing
<script type='module'>ES module script