The if_excerpt tag is a conditional tag and always used as an opening and closing pair, like this…
<txp:if_excerpt> ...conditional statement... </txp:if_excerpt>
The tag will execute the contained statements if an excerpt is associated with the article being displayed.
Display the excerpt if it exists
<txp:if_excerpt> <txp:excerpt /> <txp:else /> Section <a href="/subdirname/index.php?s=<txp:section />"><txp:section /></a> </txp:if_excerpt>
If there is no excerpt associated with the current article, the section name linked as /“subdirname/index.php?s=section_name” will be displayed instead, providing a means of displaying the articles from the same section as the current article.