An application teaches PAD new words by putting files in the right directory - no registration, no configuration. The file's name is the name in the template.

A tag of your own: _tags/

A file _tags/badge.php makes {badge} a tag. The file reads its parameters with padTagParm ( name, default ) and returns what it renders - a value, whose braces stay text; $padContent is template source, so nothing built from a parameter goes there. The app: prefix names it explicitly when another meaning of the name is in the way:

PHP HTML
fragments/extending_1.pad Result

PHP	HTML fragments/extending_1.pad	Result
	`<p>{badge label='new'/}</p> <p>{badge/}</p> <p>{app:badge label='explicit'/}</p>`	«new» «plain» «explicit»

<p>{badge label='new'/}</p>
<p>{badge/}</p>
<p>{app:badge label='explicit'/}</p>

«new»

«plain»

«explicit»

<?php                                   // _tags/badge.php

  $label = padTagParm ( 'label', 'plain' );

  return '&laquo;' . htmlspecialchars ( $label ) . '&raquo;';

?>

A pipe function: _functions/

A file _functions/stars.php makes | stars a pipe. The file gets the piped text as $value, its parameters as $parm, and returns the answer - and it chains with everything else:

PHP HTML
fragments/extending_2.pad Result

PHP	HTML fragments/extending_2.pad	Result
	`<p>{echo 'well done' \| stars}</p> <p>{echo 'well done' \| upper \| stars}</p>`	* well done * * WELL DONE *

<p>{echo 'well done' | stars}</p>
<p>{echo 'well done' | upper | stars}</p>

*** well done ***

*** WELL DONE ***

A snippet: _include/

A file _include/tip.pad is template, dropped in wherever its name is written - bare, or with the include: prefix:

PHP HTML
fragments/extending_3.pad Result

PHP	HTML fragments/extending_3.pad	Result
	`{tip} {include:tip}`	Tip: the parser likes a single tag closed with a trailing slash. Tip: the parser likes a single tag closed with a trailing slash.

{tip}
{include:tip}

Tip: the parser likes a single tag closed with a trailing slash.

Functions for every page: _lib/

Every .php file in _lib/ is included on every request, so a page's PHP half calls what they define without an include of its own:

PHP fragments/extending_4.php	HTML fragments/extending_4.pad	Result
`<?php $echoed = manualTwice ( 'hear me' ); ?>`	`<p>{$echoed}</p>`	hear me hear me

The whole family

directory	a file there is
`_tags/`	a tag
`_functions/`	a pipe function
`_include/`	a template snippet
`_lib/`	PHP functions, included every request
`_callbacks/`	a data iteration hook - see callback
`_options/`	a tag option of your own - see options of your own
`_events/`	a hook for an error, a query, a fetch or the finished page - see event hooks
`_data/`	a data file, usable as a tag - see the data tag
`_scripts/`	a shell script, run by the `script:` prefix

A subdirectory may carry any of these of its own: its pages see both, and its version of a name wins - the story of the application structure page.