CSS revert value

A CSS keyword value that resets a property's value to the default specified by the browser in its UA stylesheet, as if the webpage had not included any CSS. For example, `display:revert` on a `<div>` would result in `display:block`. This is in contrast to the `initial` value, which is simply defined on a per-property basis, and for `display` would be `inline`.

HEIF/HEIC image format

A modern image format based on the [HEVC video format](/hevc). HEIC generally has better compression than [WebP](/webp), JPEG, PNG and GIF. It is hard for browsers to support HEIC because it is [complex and expensive to license](https://en.wikipedia.org/wiki/High_Efficiency_Video_Coding#Patent_licensing). [AVIF](/avif) and [JPEG XL](/jpegxl) provide free licenses and are designed to supersede HEIC.

PNG favicons

Icon used by browsers to identify a webpage or site. While all browsers support the `.ico` format, the PNG format can be preferable.

SVG favicons

Icon used by browsers to identify a webpage or site. While all browsers support the `.ico` format, the SVG format can be preferable to more easily support higher resolutions or larger icons.

X-Frame-Options HTTP header

An HTTP header which indicates whether the browser should allow the webpage to be displayed in a frame within another webpage. Used as a defense against clickjacking attacks.

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