Here is what Melissa said in response to my suggestion that whoever writes the next manuals and help files make a correction.
"Blue is correct in that the text fields are limited to 64K. You're right that the help and manual shouldn't say unlimited. I'll make a note of it. I think that Howard Nurse used the term "virtually unlimited" because there is a limit, but 64K is about 35 pages of text and the chances of you hitting that limit was unlikely. --Melissa"