In histograms for character and datetime columns, all column data is contained in double quotes. If the column itself contains the double-quote character, optdiag displays two quotation marks. For example, if the column value is:
a quote "mark"
optdiag displays:
"a quote" "mark"
The only other special character in optdiag output is the pound sign (#), which, in input mode, means that all characters on the line following a pound sign are ignored, except when the pound sign occurs within quotation marks as part of a column name or column value.