When a document is transmitted via a [[MIME]] message or a transport that uses MIME content types such as an [[HTTP]] response, the message may signal the encoding via a Content-Type header, such as <code>Content-Type: text/html; charset=UTF-8</code>. Other external means of declaring encoding are permitted but rarely used. If the document uses ana [[Comparison of Unicode encodings|Unicode encoding]], the encoding info might also be present in the form of a [[Byte order mark]]. Finally, the encoding can be declared via the HTML syntax. For the <code>text/html</code> serialisation then, as long as the page is encoded in an extension of [[ASCII]] (such as [[UTF-8]], and thus, not if the page is using [[UTF-16]]), a <code>meta</code> element, like <code><meta http-equiv="content-type" content="text/html; charset=UTF-8"></code> or (starting with [[HTML5]]) <code><meta charset="UTF-8"></code> can be used. For HTML pages serialized as XML, then declaration options is to either rely on the encoding default (which for XML documents is UTF-8), or to use an XML encoding declaration. The meta attribute plays no role in HTML served as XML.
