The if_article_id tag is a conditional tag and always used as an opening and closing pair, like this…
<txp:if_article_id> ...conditional statement... </txp:if_article_id>
The tag will execute the contained statement if the article id associated with a particular article matches the id attribute. Should be used in an article form/container. The id attribute must be used in an article list context (when producing a page that displays more than one article) or the tag will do nothing.
id="current article's ID" (integer)