Filters

Filters work through a pair of functions that work together just like hooks.  They are:

apply_filters()add_filter()

The apply_filters() is the one that defines the filter within the WordPress code.

Line 243 of post-template.php in wp-includes has this line:

$content = apply_filters('the_content',content)

The first parameter is the name of the filter and the second is the value to be filtered.  Can pass more then one argument.

ad_filter() is to modify the value of the function .

function modify_content($content){   return $content.'Copy right 2022';
}
add_filter('the_content','modify_content');

Why its called a filter – I modify the content and then pass it back.

Doesn’t have to be together.

Accepts two parameters – the name of the filter, the seonc dis the callback function.If two – have to specify it:

add_filter('body_class','modify_body_classes', 10, 2)

third parameter is priority.  If forget # of parameters and it is greater then 1 – error!  Use same values in  add_filter() that are used in apply_filters()

 

Divides some in 2 groups – one that are read from the database first and then filtred out. or applied to info first and then snet to database.  Content one is in th eefirst.

add_filter(‘contant-save-pre’,’my_santitize_content’) does the latter