What filters are applied to the_content function?

Question

How does WordPress convert raw data from the database to a readable format in the_content function?

I've noticed that it applies the_content filter, but what does the_content filter do?

Answer 1

the default filters are set in /wp-includes/default-filters.php;

for 'the_content' this is from line 135:

add_filter( 'the_content', 'wptexturize'        );
add_filter( 'the_content', 'convert_smilies'    );
add_filter( 'the_content', 'convert_chars'      );
add_filter( 'the_content', 'wpautop'            );
add_filter( 'the_content', 'shortcode_unautop'  );
add_filter( 'the_content', 'prepend_attachment' );

to trace the individual functions, you could try and use http://phpxref.ftwr.co.uk/wordpress/nav.html?_functions/index.html then follow the links...

Edit

Missed one (wp-includes/default-filters.php, line 102):

// Format WordPress
foreach ( array( 'the_content', 'the_title' ) as $filter )
    add_filter( $filter, 'capital_P_dangit', 11 );

Answer 2

All filters are stored in the global $wp_filter variable. You can inspect that variable to see which functions are bound to a certain filter.

global $wp_filter;
print_r($wp_filter['the_content']);

To exactly understand the array that gets outputted, knowing how the $wp_filter variable is built up helps a lot. This line is from the source of the add_filter() function:

$wp_filter[$tag][$priority][$idx] = array('function' => $function_to_add, 'accepted_args' => $accepted_args);