Accelerated Mobile Pages
Accelerated Mobile Pages (AMP) are a variant of HTML promoted by Google (along with some other companies) as a way of enabling publishers to produce mobile web pages that load and render quickly and are easy to read and navigate on portable devices.
AMP documents are built with a limited subset of HTML, augmented with some AMP-specific tags to handle graphics and multimedia content. Among these specialized tags is a tag specifically for embedded ads (
amp-ad), replacing the hodgepodge of bulky and messy scripts usually used for this purpose. Images use
amp-img instead of the normal
AMP pages have a normal HTML 5 doctype,
<!doctype html>, so they are not distinguished from normal HTML this way. However, the main
html element has a special attribute,
<html ⚡>, featuring the Unicode character U+26A1, "HIGH VOLTAGE SIGN". This is a departure from usual markup-language conventions where non-ASCII characters are avoided in markup syntax (even if they are present in the text content) to avoid the various character-encoding problems that often result from their use; they are apparently presuming that everybody has "gone native" with UTF-8 and can handle a wider character repertoire. However, you are allowed to use
<html amp> if you don't want to use non-ASCII characters or have no idea how to type that lightning-bolt thingy (though you can copy-and-paste it from another place, including this page).