C-SUL has no built-in functions, and is only a list.
Copy-Safe Unicode List, by ARX. C-SUL is a compiled list of Unicode characters which do not morph or conjugate when placed together. This is especially important for preventing mutability within the output of parsers. In theory, this list should also be mobile safe as it avoids using mobile unsafe characters and any possible conjugations that may distort output data. C-SUL was compiled with the original database DUCKS and was checked for all ~800 million two character conjugations. As a result, the output decreased from 40,281 possible Unicode characters down to 12,767. However, it was necessary to reduce the amount of valid characters, as conjugation led to data corruption, something I learned from prior experience.