Why does a phpecho statement display back on a new page sometimes on the original page.

In the case of {code...}, the echo statement is displayed on the new page. However, if php statements are combined and html statements are placed later, the echo statements are displayed before the html code. why? Thank you!

  Html code

  

In this case, the echo statement is displayed on the new page.
However
Php statements are combined, and then html statements are placed,
The echo statement is displayed before the html code. why?
Thank you!

Reply content:

  Html code

  

In this case, the echo statement is displayed on the new page.
However
Php statements are combined, and then html statements are placed,
The echo statement is displayed before the html code. why?
Thank you!

The browser can only execute html code, but cannot execute php code. After the php code is executed on the server, the html content is generated and returned to the browser for display by the browser.