What is an archived article?
Archived plugins/mods/etc. are those whose functionality has been built into the Textpattern core code, or is otherwise outdated.
Using this site
All plugins, mods, etc. that are posted to this site will be kept even after they have out-lived their usefulness — perhaps their functionality has been added to the Textpattern code so that a built-in Textpattern tag can fully take the place of what used to be a plugin, perhaps the plugin worked on a very early version of Textpattern and now is incompatible with the current and recent versions.
Just because an an article is archived does not mean that its contents are completely useless and outdated. Firstly, it was likely a very valuable resource in its day, and just because new functionalities have replaced it over time does not belittle its significance to the Textpattern project/community. (Example: txp:mdn_if_custom uses ID numbers to identify custom fields, whereas the current txp:if_custom relies on field names.) Secondly, sometimes the old plugins have features that the new plugins/built-in tags do not yet cover. Or you may find it useful to use different tags and plugins (that are meant to accomplish the same thing) on the same page for nesting abilities (tags within tags), if the “current” tag does not already allow for nesting. (Example: you can nest txp:ob1_if_section, mdn_if_section, and txp:if_section to have something like:
<txp:if_section name="default,about,article,portfolio">
all of them
<txp:ob1_if_section section="!about">
all except about
<txp:mdn_if_section section="portfolio">
only if portfolio
</txp:mdn_if_section">
<txp:mdn_if_section section="default">
only if default
</txp:mdn_if_section>
</txp:ob1_if_section>
</txp:if_section>
Anyway, the point is that articles will be archived on this site to show that new options/core-code alternatives exist, but old articles, plugins, etc., will be kept.