memoQ performs spell checking on a word-by-word basis. Words, for spelling, are defined as a sequence of non-whitespace characters, surrounded by whitespace or a segment boundary. Before asking the spell check engine, memoQ first looks for the word in the active ignore lists. If the word is found in any of these, it is considered to be correct, and the spell checker itself is not invoked.
Lookup in the ignore lists is smart: if the current word is in uppercase (first or mixed or all capitals), but the list includes the same word in lower case only, that is accepted. If the current word has a trailing period, but a word (upper or lower case, as above) is in the list without a period, that is accepted. The reverse is not true: "etc." in the list will not make "etc" accepted in the text.