Accented Characters and Counting Syllables

["Nordlöw" via Digitalmars-d-learn]

On Sunday, 7 December 2014 at 15:47:45 UTC, H. S. Teoh via 
Digitalmars-d-learn wrote:
>> Ok, thanks.
>> 
>> I just noticed that byGrapheme() lacks bidirectional access. 
>> Further
>> it also lacks graphemeStrideBack() in complement to 
>> graphemeStride()?
>> Similar to stride() and strideBack(). Is this difficult to 
>> implement?
>
> Not sure, but I wouldn't be surprised if it is. Unicode 
> algorithms are
> generally non-trivial.
>
>
> T

What's the best source of information for these algorithms? Is it 
certain that graphemes iteration is backwards iteratable by 
definition?