Learn English – Singular and plural form in a section title

While these are three unrelated words, they share some characteristics: all are produced by modifying existing words in particular ways that are fairly standard.

You're right that a documenter would be one who documents; in general, adding "-r" or "-er" to a verb very often means someone who often does that verb. Your automated spell-checker doesn't have enough of a vocabulary to tell that automatically, though.

Your intuition about "web-mistress" being related to "webmaster" is also correct. But in compound words using "master", substituting "mistress" is usually not going to make anyone* think of the modern slang usage of "mistress" on its own, since the other words qualify the meaning to be a particular sort of master or mistress… and that almost always means starting from the most basic and literal sense of the word, which is still generally known by native speakers. So this coined word means nothing other than a female webmaster. (It's unlikely to be a formal job title; rather, it's most likely a somewhat whimsical title taken on by the lady herself. This sort of playful self-naming is fairly common among geeks, especially those who work more or less independent of conventional job structures.)

"Cabalesque" has a rather uncommon productive suffix, "-esque" (which means "like" or "in the manner of", and is often separated with a hyphen to make it easier to distinguish). Given that, and the way "cabal" can mean "a small group of people who work together secretly" (MW), "cabalesque knowledge" means something like "cryptic knowledge like that of some old secret societies, carefully isolated from outsiders". (Per Nelson, it can especially refer to highly specialized technical knowledge that has never been shared with those outside a small group, whether intentionally trying to keep it secret or simply not putting effort into sharing that knowledge.)

_{*Except amateur comedians on the Internet, anyway.}

This is a funny question to an Australian. Yous is commonly heard in Australia among people who are popularly referred to as bogans, but is also heard in the more regional parts of the country. A bogan is someone who is a little rough around the edges, probably poorly educated or sometimes just pretending to be (A 'bogan' who went to a private school since kindergarten is a particularly interesting phenomenon). As mentioned before though, it's not exclusive to bogans.

Anyway, it is generally seen as not proper English when used here which is funny because I hate saying 'you guys' or 'you all' and would like to be able to say "ya'll" or "youse". Sometimes I say, 'What are youse guys doing tonight?' to my friends for a laugh but as I said its usage is not widespread.

It's also spelt 'Youse' in Australia. See definition number 2: http://www.urbandictionary.com/define.php?term=Youse