|choixsiegal{value,ifyes,ifnot} will display "ifyes" of the value of the tag equals "value", and will display "ifnot" if it does not equal that value.
Example:
<BOUCLE_blog(ARTICLES) {par date} {inverse} {"<br>"}>
[<hr><h1>(#ID_ARTICLE|choixsiegal{10, "IMPORTANT", ""})</h1>]
#TITRE ...
</BOUCLE_blog>
will display the word "IMPORTANT" if the ID_ARTICLE equals "10", and will display nothing if it does not.