Release 10.1A: OpenEdge Development:
Progress 4GL Reference

’ Special character

The function of the single quote (’) is the same as the double quote. But, if you use single and double quotes in a statement, the compiler checks the outermost quotes first, giving them precedence over the innermost quotes. For example, DISPLAY ’"test"’ returns as "test". (Progress reads the double quotes literally.) And DISPLAY "’test2’" returns as ’test2’.

See also “ ” Character-string literal.