Hi,
in case you have choose fields, which reference information from another workflow you should prevent the user from entering special characters.
Example: 
A subworkflow is linked to a parent workflow with a choose field and uses the Title field as the display name.
If a user enters ; or # in the value of the field, this will break the choose field logic. The system will be interpreted as a delimiter for a new choose field.
This can be achieved by using a regular expression. 
RegEx:
^[^;#]+$
Best regards,
Daniel
                        
 
                                    