You might have seen a
array $context parameter numerous time in different
class involved in the spellchecking process.
In a pipeline logic execution like the
MispellingFinder where every step are
isolated from the other and don't share any state:
Source -> Texts -> Text Processor -> Spellchecker -> Misspellings Handler
You might need a way to pass an information from the Source step to the Misspellings Handler for your use case.
An example could be if you want to spellcheck your blog articles (the Source) and
want to send email containing the misspellings found and the related article in which they've been found (Mispellings Handler).
In that case, the Source can pass the article it's processing in the
up through the Spellchecker that will attach the context to the misspellings
found and all the way to the Misspellings Handler
An implementation of this use case can be found in Create Custom Misspellings Handlers.