On the WebSpellChecker version 5.28.4.0+ for both User and Custom Dictionaries APIs the following symbols are allowed:

A word for the dictionaries is considered valid if it contains at least one letter. Words that consist solely of numbers, apostrophes, or any other non-letter characters are not considered valid.

If you identify any inconsistencies between the information presented and what appears on your end, please inform us by contacting our support team at [email protected].