[handrous]

To be fair, in real life, I usually see it used as a straight synonym for "understand" or "comprehend", just with extra geekiness. Very rarely is its special meaning actually intended.

[prepend]

I’ve never seen it used in that way, almost always it means to completely know something on a very deep level. To know it inside and out, etc.

[xref]

Much more common is “expert” or “mastery” for that level of understanding, when I hear “grok” it means they read the Wikipedia page or did the tutorial or something.