I realized that ":-2" is ambiguous: Default value or substring? A SPC does disambiguate (now I know). I still wonder why the manual page does not change "${parameter:offset}" and "${parameter:offset:length}" to "${parameter: offset}" and "${parameter: offset:length}", respectively. Or change the wording of "If offset evaluates to a number less than zero" to "If offset evaluates to a number less than zero AND begins with a space"
You get the idea... Yes, it was all my fault. Ulrich