Meaning
A markup keyword wrapped in angle brackets that tells the browser what kind of element to create.
How to target it
Use the tag name when the target is a broad element type, such as every button or every link.
Markup
<header>...</header>Request example
Change the style of all button tags inside the header.
Meaning
A complete piece of HTML, usually made from a start tag, content, and an end tag.
How to target it
Say element when you mean one visible part of the page, such as a title, card, or button.
Markup
<button>Menu</button>Request example
Move the language switcher element next to the menu button.
Meaning
Extra information written inside a start tag, such as href, class, id, src, or aria-label.
How to target it
Attributes are useful when the same tag appears many times but only one has a specific class, id, or label.
Markup
<a href="/ko">Home</a>Request example
Add an aria-label attribute to the icon-only menu button.
Basics
Opening and closing tag
Opening and closing tag
<section>Content</section>
Meaning
Many elements start with an opening tag and end with a matching closing tag.
How to target it
This helps when explaining where a section begins and ends in markup.
Note
A missing closing tag can make the browser treat later content as part of the wrong element.
Markup
<section>Content</section>Request example
Check that the card section has matching opening and closing tags.
Meaning
A declaration that tells the browser to render the document as modern HTML.
How to target it
It is usually handled by the framework and rarely edited during component work.
Markup
<!doctype html>Request example
Do not change the document type; only edit the page component.
<html lang="ko">...</html>
Meaning
The root element that wraps the whole HTML document.
How to target it
The html element is used for document-wide settings such as language or theme attributes.
Markup
<html lang="ko">...</html>Request example
Set the html lang attribute correctly for each locale.
<head><title>...</title></head>
Meaning
The document area for metadata, title, icons, SEO tags, and scripts that are not visible page content.
How to target it
Use this term when asking to change SEO title, description, canonical URL, or metadata.
Markup
<head><title>...</title></head>Request example
Update the metadata title for the HTML structure terms page.
<body>Visible page</body>
Meaning
The document area that contains visible page content.
How to target it
Most layout, header, menu, and tool edits happen inside the body.
Markup
<body>Visible page</body>Request example
Keep the body background consistent in light and dark mode.
<title>Engineering Tools for AI</title>
Meaning
The page title shown in the browser tab and often used by search engines.
How to target it
Use it when the visible H1 is fine but the browser or SEO title needs to change.
Markup
<title>Engineering Tools for AI</title>Request example
Make the browser title more specific without changing the visible page heading.
<meta name="description" content="...">
Meaning
Metadata tags that describe the page, viewport, encoding, or social preview information.
How to target it
Meta descriptions affect previews and search snippets, not visible page text.
Markup
<meta name="description" content="...">Request example
Update the meta description to mention searchable HTML terms.
Meaning
A semantic region for introductory or top navigation content.
How to target it
Use header when targeting the site title, top navigation, theme button, language button, or menu button.
Markup
<header>...</header>Request example
Move the language switcher inside the header controls next to the menu button.
Meaning
A semantic region for major navigation links.
How to target it
Use nav when editing category links, menu groups, or page navigation.
Markup
<nav>...</nav>Request example
Group the menu links inside nav by Converter, Math, and Programming.
Meaning
The primary content area of a page. A page should generally have one main element.
How to target it
Use main when distinguishing page content from the header, footer, or menu.
Markup
<main>...</main>Request example
Keep the floating menu above the main content without pushing it down.
Page regions
section
section
<section>...</section>
Meaning
A thematic grouping of related content, usually with a heading.
How to target it
Use section when targeting a large page block, such as hero, tools, or reference content.
Markup
<section>...</section>Request example
Reduce the vertical padding of the tools section on mobile.
Page regions
article
article
<article>...</article>
Meaning
A self-contained content item, such as a card, post, reference entry, or result.
How to target it
Use article when each repeated card has its own title and body.
Markup
<article>...</article>Request example
Make each term article more compact on desktop.
Meaning
A region for supporting content related to the main content, often a sidebar or note.
How to target it
Use aside when asking for a filter panel, side navigation, or supporting note to move.
Markup
<aside>...</aside>Request example
Move the aside below the main content on mobile.
Meaning
A bottom region for legal links, secondary navigation, contact information, or closing content.
How to target it
Use footer when targeting the page bottom rather than a section bottom.
Markup
<footer>...</footer>Request example
Add a small legal link group to the footer.
Meaning
A heading element from h1 to h6 that gives structure to page content.
How to target it
Use heading level when asking to change the hierarchy, not only the visual size.
Note
Do not choose h1 or h2 only for size; use CSS for visual size and headings for document structure.
Markup
<h1>Page title</h1>Request example
Keep the page title as h1 and make card titles h2 or h3.
Meaning
A paragraph of text.
How to target it
Use paragraph when changing descriptive body text or its spacing.
Markup
<p>Description text.</p>Request example
Shorten the paragraph under the hero title.
<a href="/ko/tools/math-prompt">Start</a>
Meaning
A link element that navigates to another page, route, file, or location.
How to target it
Use anchor or link when the element moves somewhere instead of performing an in-place action.
Markup
<a href="/ko/tools/math-prompt">Start</a>Request example
Change the Browse tools link so it scrolls to the tools section.
Meaning
A group of related items, either unordered with ul or ordered with ol.
How to target it
Use list when asking to add, remove, reorder, or group repeated text items.
Markup
<ul><li>Item</li></ul>Request example
Group the menu items into category lists.
<table><tr><td>Cell</td></tr></table>
Meaning
A structured grid of rows and cells for tabular data.
How to target it
Use table when the content is true row-and-column data, not just a visual grid of cards.
Markup
<table><tr><td>Cell</td></tr></table>Request example
Use a table for truth table data instead of plain div blocks.
Content
Code block
code / pre
<pre><code>npm run build</code></pre>
Meaning
code marks code text. pre keeps line breaks and spacing for multi-line code.
How to target it
Use code block when commands or examples must keep exact spacing.
Markup
<pre><code>npm run build</code></pre>Request example
Show terminal commands in a pre/code block.
Content
Strong and emphasis
strong / em
<strong>Important</strong>
Meaning
Semantic emphasis elements. strong means importance; em means stress emphasis.
How to target it
Use these for meaningful emphasis, not just decorative bold or italic styling.
Markup
<strong>Important</strong>Request example
Use strong for the warning phrase inside the note.
<img src="/hero.png" alt="Tool preview">
Meaning
An element that displays an image file.
How to target it
Use image when asking to replace, resize, crop, or add alternative text to visual media.
Markup
<img src="/hero.png" alt="Tool preview">Request example
Add a clear alt attribute to the hero image.
<img alt="Menu panel open">
Meaning
Text that describes an image for screen readers and when the image cannot load.
How to target it
Use alt when asking to improve accessibility or image meaning.
Note
Decorative images can use empty alt text, but meaningful images need a useful description.
Markup
<img alt="Menu panel open">Request example
Add alt text that explains what the screenshot shows.
Meaning
A vector graphic element often used for icons, diagrams, and scalable shapes.
How to target it
Use SVG when the visual is a simple shape or icon that should remain crisp.
Markup
<svg>...</svg>Request example
Use an SVG icon for the menu button if there is no icon library available.
Forms and controls
Button
button
<button type="button">Menu</button>
Meaning
A control that performs an action when clicked or tapped.
How to target it
Use button when the control changes UI state, opens a menu, submits a form, or runs an action.
Note
For navigation, a link is usually better than a button.
Markup
<button type="button">Menu</button>Request example
Make the menu button close the language dropdown before opening the menu.
Forms and controls
Form
form
<form>...</form>
Meaning
A group of controls used to collect and submit user input.
How to target it
Use form when inputs belong to one submission or one input workflow.
Markup
<form>...</form>Request example
Group the search input and category controls in one form-like control area.
Forms and controls
Label
label
<label for="search">Search</label>
Meaning
Text that names a form control.
How to target it
Use label when an input needs visible or screen-reader-friendly naming.
Markup
<label for="search">Search</label>Request example
Add a label for the search input without cluttering the UI.
Forms and controls
Input
input
<input type="search" placeholder="Search">
Meaning
A field where the user types or chooses a value.
How to target it
Use input when targeting search fields, text fields, numbers, checkboxes, or other simple controls.
Markup
<input type="search" placeholder="Search">Request example
Make the search input full width on mobile.
Forms and controls
Select
select
<select><option>English</option></select>
Meaning
A native dropdown control for choosing one option from a list.
How to target it
Use select when the control is a native form dropdown, not a custom menu panel.
Markup
<select><option>English</option></select>Request example
Style the language select so the selected option is readable in dark mode.
Forms and controls
Textarea
textarea
<textarea>Long text</textarea>
Meaning
A multi-line text input.
How to target it
Use textarea when users need to paste or edit longer text.
Markup
<textarea>Long text</textarea>Request example
Increase the textarea height for long prompt input.
<button class="icon-button">...</button>
Meaning
An attribute used to group elements for styling or behavior.
How to target it
Class is often the most practical way to target a repeated UI pattern.
Markup
<button class="icon-button">...</button>Request example
Apply the same class to all menu category toggle buttons.
<section id="tools">...</section>
Meaning
A unique identifier for one element on a page.
How to target it
Use id when a link needs to scroll to a specific section or a label must connect to one input.
Note
The same id should not be reused for multiple elements on one page.
Markup
<section id="tools">...</section>Request example
Add an id to the tools section so the Browse tools link can scroll there.
<a href="/ko/reference/html-structure-terms">HTML</a>
Meaning
The destination URL or fragment for a link.
How to target it
Use href when a link points to the wrong page or section.
Markup
<a href="/ko/reference/html-structure-terms">HTML</a>Request example
Change the Programming menu href to the new HTML structure terms page.
<img src="/images/example.png" alt="Example">
Meaning
The source file path for images, scripts, iframes, and similar media.
How to target it
Use src when an image or script is missing, wrong, or should be replaced.
Markup
<img src="/images/example.png" alt="Example">Request example
Replace the image src with the new preview image path.
Attributes
Data attribute
data-*
<html data-theme="dark">
Meaning
Custom attributes used to store state or metadata on an element.
How to target it
Use data attributes when styling depends on a state such as theme, open, closed, or selected.
Markup
<html data-theme="dark">Request example
Use data-theme on the html element to switch dark mode colors.
<div role="menu">...</div>
Meaning
An accessibility attribute that describes what kind of UI object an element represents.
How to target it
Use role when a custom component needs clear semantics, such as menu, dialog, tab, or alert.
Note
Native semantic elements are usually better than adding role to a generic div.
Markup
<div role="menu">...</div>Request example
Give the custom language list an appropriate menu role.
Accessibility
aria-label
aria-label
<button aria-label="Toggle menu">...</button>
Meaning
A text label for assistive technologies when visible text is missing or insufficient.
How to target it
Use aria-label for icon-only controls such as menu, search, close, or theme buttons.
Markup
<button aria-label="Toggle menu">...</button>Request example
Add an aria-label that clearly names the hamburger menu button.
Accessibility
aria-expanded
aria-expanded
<button aria-expanded="false">Menu</button>
Meaning
An accessibility attribute that tells whether a controlled panel is open or closed.
How to target it
Use it for dropdown buttons, accordions, and menu toggles.
Markup
<button aria-expanded="false">Menu</button>Request example
Update aria-expanded when the menu category opens or closes.
Relationships
Parent and child
Parent and child
<nav><a>Link</a></nav>
Meaning
A parent element contains child elements inside it.
How to target it
Use this when the target depends on where it is located, such as links inside nav or buttons inside header.
Markup
<nav><a>Link</a></nav>Request example
Style only the links that are children of the header nav.
Relationships
Sibling
Sibling
<button /> <button />
Meaning
Elements that share the same parent are siblings.
How to target it
Use sibling when spacing or interaction depends on neighboring items.
Markup
<button /> <button />Request example
Reduce the gap between sibling header buttons.
Relationships
Nesting
Nesting
<section><article><h2>Title</h2></article></section>
Meaning
The structure created when elements are placed inside other elements.
How to target it
Use nesting when explaining exactly which inner element should change.
Markup
<section><article><h2>Title</h2></article></section>Request example
In each card, move the request example below the property chips.
Relationships
Wrapper
Wrapper
<div class="container">...</div>
Meaning
An element used mainly to group, constrain, or position other elements.
How to target it
Use wrapper when the layout needs a surrounding element rather than changes to each child.
Markup
<div class="container">...</div>Request example
Add a wrapper around the header controls so the dropdown can align to the right.
Relationships
Container
Container
<div class="container">Page content</div>
Meaning
A wrapper that keeps page content aligned and constrained to a readable width.
How to target it
Use container when changing the overall content width or side padding.
Markup
<div class="container">Page content</div>Request example
Make the main content container slightly narrower on desktop.
Relationships
Fragment
Fragment
<>...</>
Meaning
A wrapper used in React to group elements without adding an extra DOM element.
How to target it
Use fragment when grouping elements without affecting layout or CSS selectors.
Markup
<>...</>Request example
Use a fragment instead of adding an unnecessary wrapper div.
Accessibility
Semantic HTML
Semantic HTML
<main><section><h1>...</h1></section></main>
Meaning
HTML that uses elements according to their meaning, not only their visual appearance.
How to target it
Use semantic HTML when improving structure, accessibility, SEO, or maintainability.
Markup
<main><section><h1>...</h1></section></main>Request example
Use semantic HTML for the reference page sections instead of generic divs everywhere.
Accessibility
Landmark
Landmark
<header> <nav> <main> <footer>
Meaning
Important page regions that help assistive technology users navigate quickly.
How to target it
Header, nav, main, aside, and footer can act as landmarks.
Markup
<header> <nav> <main> <footer>Request example
Keep one clear main landmark on each page.
Accessibility
Accessible name
Accessible name
<button aria-label="Open menu">☰</button>
Meaning
The name assistive technology uses to announce a control.
How to target it
Use accessible name when a control is visually clear but not named for screen readers.
Markup
<button aria-label="Open menu">☰</button>Request example
Give the theme toggle a clear accessible name in every locale.
Accessibility
tabindex
tabindex
<button tabindex="0">Action</button>
Meaning
An attribute that can affect keyboard focus order.
How to target it
Use it carefully when custom controls are not reachable by keyboard.
Note
Positive tabindex values can create confusing keyboard order. Native focus order is usually better.
Markup
<button tabindex="0">Action</button>Request example
Avoid positive tabindex values and keep keyboard order natural.