GNU macro processor
3.5 Macro expansion
When the arguments, if any, to a macro call have been collected, the
macro is expanded, and the expansion text is pushed back onto the input
(unquoted), and reread. The expansion text from one macro call might
therefore result in more macros being called, if the calls are included,
completely or partially, in the first macro calls' expansion.
Taking a very simple example, if foo expands to `bar', and
bar expands to `Hello world', the input
will expand first to `bar', and when this is reread and
expanded, into `Hello world'.
