On the WebSpellChecker version 5.28.0.0 for both User and Custom Dictionaries APIs the following symbols are allowed:
- Apostrophe (0x0027), fullwidth apostrophe (0xFF07), full stop (0x002E);
- ANY letter or digit except a) modifier letter (https://www.compart.com/en/unicode/category/Lm), b) letter number (https://www.compart.com/en/unicode/category/Nl), c) other number (https://www.compart.com/en/unicode/category/No);
- ANY dash (hyphen): https://www.compart.com/en/unicode/category/Pd.
