The text to store as the rich text attribute could not be converted to Windchill format

We encountered this error message when transferring simple text comments to rich text comments. This is alluded to here: https://www.ptc.com/en/support/article/CS297322?source=search where it mentions that comments with special characters will be ignored. I am posting more as documentation rather than a question for the field. I have a customization that takes task comments and copied them to a discussion forum so it must be able to handle anything the user can submit. Looking at my logs, I think it does not like & at least but need to get a complete list. 

Caused by: org.xml.sax.SAXParseException; lineNumber: 1; columnNumber: 68; The entity name must immediately follow the '&' in the entity reference.

method that threw error was 

at com.ptc.core.richtext.HTMLText.setFormattedText(HTMLText.java:369)

https://www.ptc.com/en/support/article/CS293387?source=search

Last one found for context when descriptions were converted.