HTML

Reference cards for HTML elements: their content models, default ARIA semantics, and what passing implementations look like for users.

• HTML <details> and <summary>

  <details> is the native disclosure widget. The 2024 name attribute lets a group of <details> behave as an exclusive accordion. Replaces a long history of ad-hoc collapsible-panel JavaScript.

• HTML <form> element and submission semantics

  <form> wraps a set of controls and defines how they are submitted. Knowing the difference between native validation, the FormData API, and constraint validation prevents most form bugs.

• HTML semantic elements

  HTML's semantic vocabulary — header, nav, main, article, section, aside, figure, footer — encodes structure that browsers, search engines, and assistive technology rely on.

• The HTML <dialog> element

  <dialog> is the native HTML modal and non-modal dialog element. It manages focus trapping, the top layer, and inert background, replacing many ad-hoc modal libraries.

• The HTML <input> element and its types

  <input> with its 22 type values is the most variable element in HTML. Each type carries different validation, keyboard, and platform UI semantics. Picking the right type is the difference between mobile autofill working or not.