How to save the content of the form after going back one page in PHP_PHP Tutorial

After the php form is submitted and then retreats, the content of the form is cleared by default (when using session_start). The solution is to write

header("Cache-control: private"); (1) Open a new window
The value is private, no-cache, must-revalidate, then the server will be re-visited when a new window is opened.
If the max-age value is specified, the server will not be accessed again within this value, for example:
Cache-control: max-age=5 (indicates 5 seconds after accessing this web page) Accessing again within seconds will not go to the server)
(2) Press Enter in the address bar
if the value is private or must-revalidate, the server will only be accessed the first time, and will not be accessed again.
The value is no-cache, then it will be accessed every time.
If the value is max-age, it will not be accessed again before expiration.
(3) Press the back button. If the value of
is private, must-revalidate, max-age, it will not be accessed again. If the value of
is no-cache, it will be accessed repeatedly every time.
( 4) Press the refresh button
No matter what the value is, it will be accessed repeatedly
When the Cache-control value is "no-cache", accessing this page will not leave a page backup in the Internet temporary article folder.
In addition, caching can also be affected by specifying the "Expires" value. For example, if you specify the Expires value as a time that has already passed, then if you press Enter repeatedly in the address bar when accessing this website, the access will be repeated each time: Expires: Fri, 31 Dec 1999 16:00:00 GMT
For example : Disable page caching in IE
http response message header settings:
CacheControl = no-cache
Pragma=no-cache
Expires = -1
Expires is a good thing, if The web pages on the server change frequently, so set it to -1 to indicate immediate expiration. If a web page is updated at 1 am every day, you can set Expires to 1 am the next day.
When the HTTP1.1 server specifies CacheControl = no-cache, the browser will not cache the web page.
Legacy HTTP 1.0 servers cannot use the Cache-Control header.
So in order to be backward compatible with HTTP 1.0 servers, IE provides special support for HTTP using the Pragma:no-cache header.
If the client communicates with the server over a secure connection (https://) and the server returns the Pragma:no-cache header in the response,
Internet Explorer will not cache the response. Note: Pragma:no-cache only prevents caching when used in a secure connection. If used in a non-secure page, the handling is the same as Expires:-1. The page will be cached but marked as expired immediately.
Cache-Control message header field description
Cache-Control specifies the caching mechanism followed by requests and responses. Setting
Cache-Control in a request message or response message does not modify the cache processing process of another message. The cache instructions during the request include no-cache, no-store, max-age, max-stale, min-fresh, only-if-cached, and the instructions in the response message include public, private, no-cache, no-store, no-transform, must-revalidate, proxy-revalidate, max-age. The meaning of the instructions in each message is as follows:
Public indicates that the response can be cached by any cache area.
Private indicates that all or part of the response message for a single user cannot be processed by the shared cache. This allows the server to only describe a partial response from a user that is not valid for other users' requests.
no-cache indicates that the request or response message cannot be cached.
no-store is used to prevent important information from being released unintentionally. Sending it in the request message will cause both the request and response messages to use caching.
max-age indicates that the client can receive responses with a lifetime no greater than the specified time in seconds.
min-fresh indicates that the client can receive responses with a response time less than the current time plus the specified time.
max-stale indicates that the client can receive response messages beyond the timeout period. If you specify a value for max-stale messages, the client can receive response messages that exceed the specified value of the timeout period.

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