Here's a short explanation of
the configuration directives.
filter.defaultstring
Filter all $_GET, $_POST,
$_COOKIE, $_REQUEST and
$_SERVER data by this filter.
Original data can be accessed through filter_input.
Accepts the name of the filter you like to use by default. See the
existing filter list for the list
of the filter names.
Note:
Be careful about the default flags for the default filters. You should explicitly
set them to the value you want. For example, to configure the default filter to
behave exactly like htmlspecialchars you need to set them
default flags to 0 as shown below.
Example #1 Configuring the default filter to act like htmlspecialchars
Default flags to apply when the default filter is set. This is set to
FILTER_FLAG_NO_ENCODE_QUOTES by default for backwards
compatibility reasons. See the flag list
for the list of all the flag names.