Is this included as standard HTML?

Welcome to using includes via trying a common header

require is like include but it will issue an error if it can't find the file

Both the include and require statements come with a _once version.
As the names suggest, the include_once and require_once statements only "copy and paste" the code into the file once. These statements are useful in cases where the same file may be included more than once accidentally (for instance, when the script is so long you have lost track of whether you have included the file previously).

HOWEVER --> require_once would need to be used each time... it doesn't seem to override the first instance.