When is content.php called in wordpress twentyfifteen theme?

[colap]

https://core.trac.wordpress.org/browser/branches/4.2/src/wp-content/themes/twentyfifteen/content.php

 

When is content.php called?

 

Thanks

[QuickOldCar]

In index.php of that theme or other wordpress themes usually, unless they include other files or functions special for a theme.

 

get_template_part() is the function that includes other files into the template.

 

In twentyfifteen theme it's get_template_part( 'content', get_post_format() );

[colap]

In index.php of that theme or other wordpress themes usually, unless they include other files or functions special for a theme.

 

get_template_part() is the function that includes other files into the template.

 

In twentyfifteen theme it's get_template_part( 'content', get_post_format() );

If get_post_format() returns "Standard" format, then will it be "content-get_post_format()" ?

[QuickOldCar]

get_post_format() actually returns a true/false boolean.
 
Wordpress theme functions consider this as standard.
 
get_template_part('content',get_post_format());
would be
get_template_part('content',false);
 
Since get_template_part expects a string, you would leave it empty or add a string name there.
If you wanted to keep it the same throughout a theme could define format as standard with a check.

$format = get_post_format();//boolean true/false

//do a check for true or false and assign it a string
if ( false === $format ) {

	$format = 'standard';

}
get_template_part( 'content', $format );

 
The second function variable is optional, but if used the code above would look for content-standard.php, adding it to the content area.
So add a file named content-standard.php
 
 
If you want to assign get_template_part() with different strings, should use get_post_format_string()

get_post_format_string('standard');
 
And here is the function within wordpress post-formats.php for that to see your available options

function get_post_format_strings() {
            $strings = array(
                    'standard' => _x( 'Standard', 'Post format' ), // Special case. any value that evals to false will be considered standard
                    'aside'    => _x( 'Aside',    'Post format' ),
                    'chat'     => _x( 'Chat',     'Post format' ),
                    'gallery'  => _x( 'Gallery',  'Post format' ),
                    'link'     => _x( 'Link',     'Post format' ),
                    'image'    => _x( 'Image',    'Post format' ),
                    'quote'    => _x( 'Quote',    'Post format' ),
                    'status'   => _x( 'Status',   'Post format' ),
                    'video'    => _x( 'Video',    'Post format' ),
                    'audio'    => _x( 'Audio',    'Post format' ),
            );
            return $strings;
    }