Apostrophes can either precede or follow a formal argument name in the macro source.
If an apostrophe precedes the argument name, the text before the apostrophe is concatenated with the actual argument when the macro is expanded. If an apostrophe follows the formal argument name, the actual argument is concatenated with the text that follows the apostrophe when the macro is expanded. The apostrophe itself does not appear in the macro expansion. To concatenate two arguments, separate the two formal arguments with two successive apostrophes. Two apostrophes are needed because each concatenation operation discards an apostrophe from the expansion.