Position structure for utrans_transIncremental() incremental transliteration. This structure defines two substrings of the text being transliterated. The first region, [contextStart, contextLimit), defines what characters the transliterator will read as context. The second region, [start, limit), defines what characters will actually be transliterated. The second region should be a subset of the first.
After a transliteration operation, some of the indices in this structure will be modified. See the field descriptions for details.
contextStart <= start <= limit <= contextLimit
Note: All index values in this structure must be at code point boundaries. That is, none of them may occur between two code units of a surrogate pair. If any index does split a surrogate pair, results are unspecified.