Boolean Attributes

Webflow's Custom Element appears to automatically recognize and handle boolean attributes. These can be bound to a data source. Any non-NULL value will render the value-less attribute, and NULL values will suppress it.

ere’s a comprehensive list of all standard boolean attributes in HTML. These attributes are true when present, regardless of value, and false when absent.

Notes:

• Boolean attributes do not require a value.

• Setting them to "false" does not turn them off — omit the attribute instead.

This determination does not appear to be smart about the tag used, e.g. disabled will be recognized and handled as a boolean attribute even on HTML tags that do not support disabled as a boolean attribute.

Full List of Boolean Attributes in HTML

Haven't tested any except required and checked.

But here is a cGPT list;

Attribute	Applies To	Effect When Present
allowfullscreen	<iframe>	Allows fullscreen rendering
async	<script>	Executes script asynchronously
autofocus	<input>, <textarea>, <select>	Sets focus on page load
autoplay	<audio>, <video>	Starts playback automatically
checked	`<input type="checkbox	radio">`
controls	<audio>, <video>	Displays playback controls
default	<track>, <optgroup>, <option>	Marks as default selection
defer	<script>	Defers execution until HTML parsing completes
disabled	Form elements	Disables input or control
formnovalidate	<button>, <input type="submit">	Prevents form validation on submit
hidden	All elements	Hides the element from view/rendering
inert	All elements (experimental)	Makes the element and its children non-interactive
ismap	<img>	Makes image a server-side image map
itemscope	Any element	Declares microdata item
loop	<audio>, <video>	Repeats playback automatically
multiple	<select>, <input type="file">	Allows multiple selections
muted	<audio>, <video>	Mutes media
nomodule	<script>	Prevents execution in module-supporting browsers
novalidate	<form>	Disables form validation
open	<details>	Expands the disclosure widget
playsinline	<video>	Plays video inline instead of fullscreen
readonly	<input>, <textarea>	Prevents user editing, but allows focus
required	<input>, <select>, <textarea>	Makes field required for form submission
reversed	<ol>	Reverses the list order
selected	<option>	Pre-selects the option
tristate	Custom use, not standard	Sometimes used in ARIA contexts (not native)
translate	All elements	Indicates if content should be translated (yes/no)
typemustmatch	<object>	Requires correct MIME type

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⚠️ Notes:

• Boolean attributes do not require a value.

• Setting them to "false" does not turn them off — omit the attribute instead.