Macros are not really a type of host element, but are instead configuration snippets used in source, destination and next action elements to represent dates, times, filenames and task parameters. For example, a task using a macro of "data[yyyy].log" would run against a value of "data2003.log" instead.
Macros can be used in the following places:
Macro keywords are always found in square brackets ("[","]"). Macro arguments (usually a DateSpec or an integer) follow macro keywords after a colon (":").
In some cases, task or global parameters may contain macros. These are still interpreted as macros. For example, if a global parameter named "Error_Subject" is set with a value of "ERROR in '[TaskName]' at [hh]:[mm]:[ss]", a Next Action subject set to "[Parm:Error_Subject]" would be interpreted as "ERROR in 'Get TPS Reports' at 12:34:56" when the task is run.