PHP: header - Manual
https://www.php.net/manual/ru/function.header.php
header("HTTP/1.1 404 Not Found"); I had big troubles with an Apache/2.0.59 (Unix) answering in HTTP/1.0 while I (accidentially) added a "HTTP/1.1 200 Ok" - Header. Most of the pages were displayed correct, but on some of them apache added weird content to it
HTML header Tag
https://www.w3schools.com/tags/tag_header.asp
The <header> element represents a container for introductory content or a set of navigational links. Related Pages. HTML DOM reference: Header Object. Default CSS Settings. Most browsers will display the <header> element with the following default values
Header - Wikipedia
https://en.wikipedia.org/wiki/Header
Header may refer to: Header (computing), supplemental data at the beginning of a data block. E-mail header. HTTP header. Header file, a text file used in computer programming (especially in C and C++). A pin header is a mainly male style of electrical connector on printed circuit boards...