## 3.15. Expirations

Apache Version 1.2 brought the `expires` module, mod_expires, into the main distribution. The point of this module is to allow the webmaster to set the returned headers to pass information to clients' browsers about documents that will need to be reloaded because they are apt to change, or alternatively, that are not going to change for a long time and can therefore be cached. There are three directives.

### 3.15.1. ExpiresActive

>     ExpiresActive [on|off]
>     Anywhere, .htaccess when AllowOverride Indexes

`ExpiresActive` simply switches the expiration mechanism on and off.

### 3.15.2. ExpiresByType

>     ExpiresByType mime-type time
>     Anywhere, .htaccess when AllowOverride Indexes

`ExpiresByType` takes two arguments. mime-type specifies a MIME type of file; time specifies how long these files are to remain active. There are two versions of the syntax. The first is:

>     code seconds

There is no space between code and seconds. code is one of the following:

`A`

  Access time (or now, in other words)

`M`

  Last modification time of the file

seconds is simply a number. For example:

>     A565656

specifies 565656 seconds after the access time.

The more readable second format is:

>     base [plus] number type [number type ...]

where base is one of the following:

`access`

  Access time

`now`

  Synonym for `access`

`modification`

  Last modification time of the file

The `plus` keyword is optional, and type is one of the following:

- `years`

- `months`

- `weeks`

- `days`

- `hours`

- `minutes`

- `seconds`

For example:

>     now plus 1 day 4 hours

does what it says.

### 3.15.3. ExpiresDefault

>     ExpiresDefault time
>     Anywhere, .htaccess when AllowOverride Indexes

This directive sets the default expiration time, which is used when expiration is enabled but the file type is not matched by an `ExpireByType` directive.

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