ruud suggests:

Leaving out the name attribute and setting the name attribute to an empty
string doesn’t work consistently in both tags:

* compare <txp:if_section> to <txp:if_category>: the former condition is
true on the frontpage where there is no section while the latter condition
is false on the frontpage where there is no category, but true for any
valid category. The <txp:if_category> behaviour makes more sense.

* compare <txp:if_category name="">, <txp:if_section name="">,
<txp:if_category name=",about"> and <txp:if_section name=",about">. The
last three are consistent in behaviour. When specifying an empty category
or section, if you’re on the frontpage (no section/category), the condition
is true. But <txp:if_category name=""> behaves differently, because that
one is true currently if you’re on any valid category page. An empty
category or section name could mean “any” or “none”. The latter makes more
sense and is used in 3 out of 4 situations.


related discussion: http://forum.textpattern.com/viewtopic.php?id=29263