Last year I was working at Swift to add support for Localization of Compiler Diagnostic Messages. We are currently using YAML as the new diagnostic format. The LLVM::YAMLParser didn't have a support for multiline string literal folding and it's crucial to have that for the diagnostic message to help us keep up with the 80 columns rule. Therefore, I decided to add a multiline string literal folding support to the YAML parser.
Not too deep into the YAML world, so just my two cents re the isLineBreak function.
shouldn't this rather be a check whether the line is _empty_ -> whether it contains anything else than \n\r\t ?
This would be easily solvable by using something like:
for(auto Position = Line.begin(); Position != Line.end(); ++Position) if(!isBlankOrBreak(Position)) return false; return true;
Renaming the function to isLineEmpty might sense then, too.