CSS ::marker pseudo-element

The `::marker` pseudo-element allows list item markers to be styled or have their content value customized.

Custom Elements (deprecated V0 spec)

Original V0 version of the custom elements specification. See [Custom Elements V1](#feat=custom-elementsv1) for support for the latest version.

Custom Elements (V1)

One of the key features of the Web Components system, custom elements allow new HTML tags to be defined.

Datalist element

Method of setting a list of options for a user to select in a text field, while leaving the ability to enter a custom value.

dataset & data-* attributes

Method of applying and accessing custom data to elements.

Dialog element

Method of easily creating custom dialog boxes to display to the user with modal or non-modal options. Also includes a `::backdrop` pseudo-element for behind the element.

Selectlist - Customizable select element

Proposal for a customizable `<select>` element, currently defined as `<selectlist>`, previously `<selectmenu>`.

customelementregistry api

customelementregistry api: customized built-in element support

customelementregistry api: define

customelementregistry api: define: supports `disabledfeatures` static property

customelementregistry api: get

customelementregistry api: getname

customelementregistry api: upgrade

customelementregistry api: whendefined

htmlbuttonelement api: setcustomvalidity

htmlfieldsetelement api: setcustomvalidity

htmlinputelement api: setcustomvalidity

htmlobjectelement api: setcustomvalidity

htmloutputelement api: setcustomvalidity

htmlselectelement api: setcustomvalidity

htmltextareaelement api: setcustomvalidity

window api: customelements

html element: iframe: sandbox: `sandbox="allow-top-navigation-to-custom-protocols"`