From WikiWikiSuggestions

Should I SpellCheckTheDiff, i.e., just the new part of a page? -- WardCunningham

''Or only put the unrecognized words from the diff at the top of the list, separated from the rest. Those who only want to check their contribution only look at the first part, those who want to check the whole page read the whole list.''

	 :	Well, it wouldn't be an issue if the spell-checker showed the misspelled words in their proper place in the document, giving you a visual clue as to where the errors are. If these are drop-down boxes allowing you to fix them all in seconds without a tedious find-words and re-edit cycle, then why go through the trouble of spell checking just diffs? What do you gain except fewer annoyances and right now, I don't see the spell checker as anything else but an annoyance to the users. Hmm .. I got deja vu bad and I  don't know why. Anyway, I've done the work of writing a new spell checker if you are interested. -- EvanLanglois

If I have time, I correct all the typos/misspellings diagnosed by the SpellingChecker, and would not want part of the text to be excluded. I also, from time to time, search for a common misspelling, and then correct all the affected pages. For example, I'm gradually eliminating instances of "because" and "language" misspelt with the second and third vowels exchanged. It would be acceptable to be given a two-part listing, but much more useful to have, as an option, perhaps, a page display with the "errors" in red (say). 
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When I use my Browser on Windows7, and I am in this wiki's editbox, the system highlights both misspelled and unrecognizeable (in the dictionary) words and underlines them with a squiggly-red-line. If I double-right-click the highlighted word, the pop-down menu suggests correct spelling matches, or near-matches. Choosing one of these will replace the word with the selected-word. All of this without requiring anything else from the WikiServer. There are other ways to use a SpellChecker than merely to correct misspelling. Careful and wise use of the AddToDictionary choice along with a system under which you do so, adds another indistinguishable from magic tool to the WikiToolBox. -- DoingStuff.DonaldNoyes.20121017