Programming Syntax For PhpBB Forum

I would like to know more about the syntax for phpBB, for example the code below :

    <div id="site-description"> 
<a href="{U_INDEX}" title="{L_INDE开发者_运维知识库X}" id="logo">{SITE_LOGO_IMG}</a>

                    <h1>{SITENAME}</h1>
                    <p>{SITE_DESCRIPTION}</p>
                    <p class="skiplink"><a href="#start_here">{L_SKIP}</a></p>
 </div>

I have 2 questions -

1.) How do the program define the data inside {xxx}?

2.) Where is the files located or what is the file name to define the data inside {xxx}

Thanks for helping.

{L_*} is language syntax and it located in the languages folder.When the tag starts with L_ it recognise it as a language variable, else its recognised as a variable specified from the source. The template tags {} are defined in includes/template.php

If you have a page named page.php and with defined phpbb in it, you can create own tag and use it on own template.There are global tags in includes/functions.php and private for each file (like in viewtopic.php there is postrow. template prefix).

See http://wiki.phpbb.com/Template.assign_vars for making and using such template tags.