Randall Munroe supplements the xkcd website with a Google search bar for users to search within the comics themselves by keyword, title, or the comic's transcript. However, pieces of certain transcripts may yield results that were unintended by the users; since users cannot view the transcripts alone, they are unable to see what terms are used within them and adjust their searches accordingly. This can create an issue when trying to locate one specific comic that remains lost among multiple others with similarities.
XSXKCD interprets and decides what we believe the most logical key phrases would be for users who wish to locate comics via searching. With our tags, we will pull identifiable characteristics from each comic that might not be searchable through Munroe's engine. One example is if a user wishes to locate all comics that utilize color in some way. With our tagging system, we will have identified all the xkcd comics that use color. This is not a searchable term in Munroe's system (when searched, it only pulls comics that use the word "color," not color itself).
Though that isn't to say that Munroe's search engine is unacceptable or flawed; it merely searches for things physically written into the comics. XSXKCD puts a little more human thought into our search queries and tags, making it much more manageable (and successful) for users.
The specific group of users for xkcd has also been taken into account. At the bottom of every comic, Munroe has written, "Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors)." At face value, many people could misinterpret this as meaning that only people exactly like Munroe -- that is, NASA-level intelligence and maturity -- may find this comic appealing. However, its popularity shows that clearly this is not the case. It's interesting that Munroe explicitly states who these comics supposedly aren't for, though it's probably safe to say that few have heeded his advice.
On the other hand, though, users do have to have a certain level of intellect to enjoy (and understand) all of Munroe's comics. Several of them are heavy-handed with advanced science and mathematics, and some of these users, like the poor liberal-arts majors, may be unable to fully grasp the jokes Munroe is making. So there is a bit of truth to Munroe's statement, but there are also hundreds of other comics that people who aren't as well versed in science and math as Munroe can easily enjoy. It's through these comics that Munroe can bring his disclaimer full-circle, quietly teasing those users who don't quite understand what is going on in a certain comic.
XSXKCD doesn't want to rip off xkcd; we merely want to expand its current collection and make it more accessible to those who use the source site. XSXKCD will not allow users to browse one-by-one through comics like on xkcd; the only browsing that can be done by users will be within their tag choices. It will complement the collection and give users a chance to discover, and rediscover, comics they may have missed, or a group of comics they're interested in reading.
The website itself is extremely easy to use: simply think of a search term that you believe describes the comic(s) you're searching for, and search! Though Munroe "excludes" certains audiences from his comics, we know that users from all different groups are interested in xkcd comics, including those with different technology intelligences, and XSXKCD wants to be easy to use for all users.