(Taken out of the BQM87-context:)
Charles: (...This issue is) a very big one. Anyone with a well-developed sense of what we mean by context for joseki is probably quite strong (amateur dan level) already. The joseki choice question seems to be fundamental: when you know some good sequences from a local point of view, how do you recognise how they 'fit' into the board position? I have been sceptical in the past about problems at the level of The Great Joseki Debates; Whole Board Thinking in Joseki, which is systematic, can tell you more. A good exposition of 'context' in go would be an excellent book.
Assuming a joseki will be played out in the lower right corner, we can take out a 10x10 sub-board there and wonder about all the factors in the remaining gnomon (L-shape) that could affect it.
The most usual ideas come down to saying that the adjacent corners matter most.
For example these adjacent formations have implications: the presence of (low and solid) means that any influence Black builds along the lower side may go to waste. On the other hand a joseki result that gives White a weak group developing towards the circled point is likely to be good for Black in expanding a framework based on .
In the case of this cross-hoshi formation, you can therefore predict that Black will want to play fighting joseki in the lower right: the appearance of weak white groups anywhere along the bottom or right sides should favour him.
This kind of reasoning goes one step beyond side patterns. I actually think one should probably study side patterns first, at least until the urgency of plays considered on a whole-side basis becomes reasonably clear. That might be just as important as joseki study.
Context clearly does include any relevant long ladders (which will relate to the diagonally-opposite corners). Normally ko threats aren't required in corner openings, but in middlegame joseki they definitely matter. (Context for middlegame joseki can involve just about any aspect of strategy.)
See also joseki context - different pincers.