The most recent version of this documentation can be found at https://docs.dyalog.com/20.0/.
Characters
Characters are entered within a pair of APL quotes. The surrounding APL quotes are not displayed on output. The APL quote character itself must be entered as a pair of APL quotes.
Examples
'DYALOG APL' DYALOG APL
'I DON''T KNOW' I DON'T KNOW
'*' *